Navien CH210ASME- burner cuts out for an instant

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MikeG88

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I have a Navien CH210ASME-LP that was installed just over a year ago (my builder swapped it out on their dime for a CH210(non ASME) that had the 2 second burn time problem that he couldn't solve- verified gas pressure multiple times, swapped air pressure sensor, changed burner rods etc, but they never tried to adjust the gas mixture screws). My current concerns with this unit is that sometime when thermostat calls for heat the unit ramps up for a short period but at the point where it would normally "shift gears" the green burner light on the control pad occasionally goes out and comes back on (usually an instant or so later)Seems to do this more often if DHW was recently used. The other time it does this is when it gets up to the set point temperature- the burner light may go out- it comes back on after a varying time (or ofter the T-stat will be satisfied shortly after the flame shuts off therefore no need to restart). I've been told that the later may have to do with the unit not being able to "turn down" as fast as it wants when it hits the target, so it restarts the flame and may allow a short time in between. I'm wondering if this is true and may also be the reason that it sometimes does it near the beginning. (It doesn't sit there and do it repeatedly like the 2 second burn time problem I previously had with the old unit- as well as others on this forum- so I am naturally concerned)

I am running the unit at 60% capacity, with a Taco pump set to slow- that speed was recommended I believe because return was coming back too fast- it's a single zone and house is only 24 x 48. The exhaust is plumbed for the higher temp and the board is set for that. I am running it with a Honeywell heat only thermostat set to 3 cycles per hour. I do NOT have the outdoor reset. I have tried different supply temperatures from 180 down to 150.

I am in Middlesex county, Connecticut. The house is a single level ranch (modular construction) on a full basement (walk on on one end). It has 1152 sf of area. It's not even four years old yet, obviously 2x6 walls R20 and R49 in the ceiling. If I add up all the BTU requirements on the Heat Loss Calculation page of the plans I get 28,196 BTU. But is says that its 90 deg. Design Temp. Diff. (and) Design based on 180 deg water temp at 3 GPM. If I am interpreting that correctly- it would mean that at 70 deg inside it would only need that much BTU when it is 20 below outside (70 inside - 90 differential = 20 below)? Being a modular they may use 20 below as a design temp because house could be "set" anywhere. The calculation page calls for 51LF of baseboard - there is actually 54LF installed (and I keep the louvers open on all of them).

I asked the builder if this unit was over-sized for this house and I was told the size is really based on the DHW that could be potentially called for (2 bath rooms, washer, dishwasher etc). I haven't noticed the burner cycle off and back on when using DHW - I've opened multiple faucets and checked -but burner light always appears to be on.
 
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Dana

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Is there a question in there somewhere?

The 99% outside design temp in New Haven is +7F, in New London it's +9F, so your's is probably in-between. So with a code-min interior design temp of 68F that's difference of 60F, not 90F. If you multiply the 28,196 BTU/hr @ 90F delta by 60/90 it come in at 18,797 BTU/hr which is in the right ball park (if the very high side of the ball park) for the design heat load of a house that size & construction. Reality is probably less than 15,000 BTU/hr @ +8F, maybe even as low as 12,000 BTU/hr depending on the particulars.

The MINIMUM firing rate output of the CH210ASME , is about 19,000 BTU/hr in condensing mode 17,000 BTU/hr at high-temp, which means it will never really modulate in heating mode.

You may need the bigger burner for satisfactory hot water performance with two simultaneous full-flow showers running, but it's ridiculously oversized for the space heating load, and really almost all wall-hung low mass combi boilers would be.

The water temperature required is a function of how much radiation you have for the amount of load you have. At 19,000 BTU/hr min fire output into 54' of baseboard that's 352 BTU/hr per foot, which balances at about 145-150F average water temp. So assuming a small delta-T on the heating loop anything below ~150F would cycle. But that's well above the condensing zone. The non-condensing output of about 17,000 BTU/hr at min fire into 54' of baseboard comes out to 315 BTU/hr per foot, which balances at an AWT of about 140F. So, based on the napkin-math you should be able to get the thing to run continuous burns during a call for heat with the output set to 140-145F, and it would be enough to cover the heat load down to about 0F.

If the circulation pump is an old-school 3 speed it may not be possible to get the circulation low enough to make the thing run without cycling. Replacing it with a smart-pump set to 1.5-2 gpm, or operating at a delta-T you might have an easier time taming it. The Honeywell thermostat limiting the number of cycles per hour isn't really buying you anything, and is probably only hurting the situation.

With the boiler set to 140-145F out and a smart radiation pump set to delta-T of 15-20F or ~1.5-2 gpm you may be able to operate in the condensing zone with continuous burns during calls for heat, and still have enough heat for design day. If the heating water is whizzing around at 3 gpm+ at a low delta-T the burner will almost certainly be cycling.
 

MikeG88

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Thanks Dana- The whole thing was a question and I think you explained the answer pretty well. Having lurked here for a long time- I learned that the common installer mistake of set the supply for 180 and walk away wasn't the right way to set up one of these units. You basically confirmed the theory I was heading in temperature wise with logic, math and experience to back it up. I am looking to find a local plumber to perform the factory recommended periodic maintenance on the unit and I will discuss the smart-pump with him or her. It sounds like a better alternative than a buffer-tank.
 

MikeG88

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Early this morning I noticed that the unit was short cycling and it was set at 150, so I tried 145 and then 140. It still short cycled- flame shut off, temps cooled down, flame came back on all before T-Stat was satisfied. So I turned it up to 160- it still short cycled but the T-Stat was soon satisfied so the flame didn't come back on. I know this is anecdotal but I have noticed similar pattern before. I am assuming it's because the system builds up a lot of heat at the higher temperature (before the flame shuts down) and is still "throwing" it off and radiating it. Until I can get a smart-pump installed- am I actually better off running at a higher temperature to cut down on restarts and run time on the pumps etc? At this point I am not too worried about propane usage, I am more concerned about wear and tear on the unit, I know they don't last forever, but would like to get several years out of it and see what is available then- as you said "really almost all wall-hung low mass combi boilers would be"-"ridiculously oversized for the space heating load".

As far as a Thermostat- what should I be using with one of these units? The Honeywell (builder supplied) is a heat only T87K. It is only capable of 1, 3, 5, and 9 CPH. By what I have read with these units it seems you are better off maintaining a constant temperature than letting the house cool down at night or when away (takes more energy to get back to 68-70 than you save), so I am not really interested in the need for that type of "programming". But what kind of parameters should I be looking for: a specific start and stop temperature or hold within a range etc? Is there a specific model(s) that are ideal for this type of unit? I don't need fancy internet/remote control etc. Just set for 68 or 70 and it keeps it there.
 

Jac04

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I have a Navien CH210ASME-LP ... My current concerns with this unit is that sometime when thermostat calls for heat the unit ramps up for a short period but at the point where it would normally "shift gears" the green burner light on the control pad occasionally goes out and comes back on (usually an instant or so later)Seems to do this more often if DHW was recently used. ...

I am running the unit at 60% capacity...

I have a CH-180ASME LP, and have been tinkering with it for the past 2 years. My unit would also have the occasional "shift gears" flame-out, especially when firing after it has not fired for a while. Nobody could figure it out. It always seemed to me that the unit was firing too hard trying to bring the temp up on a call for heat, and that would result in the flame going out (maybe from the blower not spooling down quick enough?). Anyhow, that was my thought. So, I now have the max firing rate set for 50%. I have been keeping a close eye on it, and I haven't noticed the problem since. Maybe try a lower max capacity setting?

By the way, when I changed my max firing rate to 50%, I also changed the DHW max firing rate to 80%. This seems to help with water temperature stability. But, you mentioned that you thought there may be a connection between DHW use and the "shift gears" flame-out, so I thought this was worth mentioning
 
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MikeG88

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To me it seems to happen more when the unit/system is already warm. It just did it to me on the first space heat call after taking a shower (have noticed that pattern before- but not necessarily after DHW usage). I believe somebody at factory support told me it has to do with the unit not being able to turn down or modulate down fast enough (although you don't always get the same answer twice from them). I guess this is different than the short cycling. I have the capacity set for 60% now and have tried lower (at least down to 50%)- exactly what does lowering the capacity do? To me it seems like it slows down the start-up- more slow and steady than jack-rabbit? Once the unit gets up to the set operating temperature I assume the actual BTU output is the same- don't want to turn down capacity too far and find unit not being able to keep up...

My previous unit had the 2 second on/off/on/off with occasional error code 12. This seems to only happen once when it does happen- and its been firing for longer than just 2 seconds when it does this. I assume the old problem was gas/air adjustment related. This seems to be more related to it heating up too quick. (After the nightmare with the old unit- I still get flashbacks with anything that seems amiss with this one)
 

Jac04

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There are 2 different max firing rates that you can adjust:
1) Heating max firing rate. Whatever you set it to is the maximum firing rate that it will be limited to. It will never go above what you set it to when calling for heat. I tried 30%, but it took much too long for my supply temperature to reach the set point, and I was worried that I wouldn't be able to keep the house at temperature when 0F outside.
2) DHW firing rate (the manual calls this 'capacity control of the whole'). This limits the max firing rate for DHW only. I have played around with it and it works. I set it to 30% and jumped into the shower. I had to keep the water on full hot, and it gradually became colder & colder, so I knew 30% was too low. I just picked 80% for a setting and everything seems fine. This setting should have no effect on the heating side of things.

The "shift gears" flame-out that you are describing is exactly what mine would do. It wouldn't do it all the time, and there didn't really seem to be a specific set of circumstances that would cause it, other than it would only do it on start-up when firing hard and getting to the 'ramp down' point. I know it's not fuel supply related on mine, because my LP piping system is done right, and I've watched dynamic supply pressure during a few of these flame-outs.

This brings up other questions. Did you make any changes to your gas supply system prior to installing the new unit? Has dynamic supply pressure been verified? Has anyone adjusted the gas/air ratio on your unit? Like I said, my problem isn't LP supply related, so I'm kind of assuming yours isn't either. But, these units are very sensitive to fuel supply.

***side note***
I'm on my 2nd CH-180ASME - my first one had the on/off/on/off start-up and error012 problem - just like yours. Mine would also rumble like a freight train on a call for DHW. Although the installer & propane company said everything was OK with fuel supply, I took it upon myself to research & properly size the propane system. Turns out the system was way undersized. I fired (no pun intended) the propane company and got another company in who completely agreed with my evaluation. I was able to get a proper new propane supply system installed right before the new CH-180ASME was installed. When the new unit was installed & worked fine, the installer blamed all the original problems on a faulty unit. What an idiot that guy was. He ended up reimbursing me for what I spent on the new propane system.
***end side note***

Also, some units were known to have questionable ground connections, so I removed the paint from under the ground screw but that didn't have any effect on the problem. However, this is one other thing to check.

The explanation of the unit not being able to turn down fast enough makes sense. I just don't know why it doesn't flame-out consistently if that is the case. While the weather is warm, you could try setting the capacity to 30% and see if it still does it. If it solves the problem, then we know it's probably a turn-down issue.

I have discussed this problem with several techs at Navien (call early from the East coast to ensure you get a tech on the west coast - they appears to be much more knowledgeable & willing to help a homeowner). I even had an expert out to the house under warranty who double-checked all the pressures & adjustments on the burners (he found nothing to be changed). They all said "don't worry about it" because it happens intermittently. The unit itself doesn't 'see' this as a problem either, otherwise an error code would be generated.

Some interesting information according to the Operation Flow Chart in the Service Manual:
You need flame-out within 10 seconds for 3 straight times to give you the 003E Ignition Failure error.
You need to loose flame 20 straight times during normal burner operation to get the 012E Flame Loss error code.
 
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Dana

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Thanks Dana- The whole thing was a question and I think you explained the answer pretty well. Having lurked here for a long time- I learned that the common installer mistake of set the supply for 180 and walk away wasn't the right way to set up one of these units. You basically confirmed the theory I was heading in temperature wise with logic, math and experience to back it up. I am looking to find a local plumber to perform the factory recommended periodic maintenance on the unit and I will discuss the smart-pump with him or her. It sounds like a better alternative than a buffer-tank.

What you're looking for is a hydronic heating person with modulating condensing boiler experience (preferably a Navien certified installer), not a random plumbing & heating company.

Just about any dumb thermostat that doesn't have a cycles per hour limiter would work. When you limit the number of cycles per hour the room temps have bigger temperature undershoots as it waits for the time-out. Having it call for heat multiple times per hour is less disruptive than having the boiler short-cycling during calls for heat.

If it's short-cycling (= burn durations of less than 200 seconds, and more than 5 burns per hour) during calls for heat with 160F output it means it's modulating much higher than it's minimum firing rate. At 160F out/140F back (150F AWT) fin-tube baseboard is delivering about 375 BTU/hr. Times 54' of baseboard that's 20,250 BTU/hr of output, which at 87% efficiency would be 20,250/0.87= 23,276 BTU/hr input, on a boiler that should be able to modulate down to 20,000 BTU/hr. That's about 15% higher than it should be. While the thermostat will be satisfied more quickly with it set to 160F, it's not clear if will actually have many fewer burn cycles during a call for heat. Satisfying the thermostat quickly isn't a virtue with a modulating system- the ideal is nearly continuous burns. Due to the oversizing factor, your goal should be to run it with a modest number of burn cycles at or near min-fire, but a nearly continuous call for heat. The thermal mass of the house is high enough that at min-fire the thing will never satisfy the thermostat quickly, but that isn't an indication that it can't keep up when it's 5-10F outside.

The "Heat Capacity Control" setting on the Navien limits the firing rate on a heating-0nly burn to percentage of the maximum, which would allow more of the burner range to be for the domestic hot water. In your case 30% (the lowest setting) of the ~175K heating BTU is about 53K, which is still more than twice your actual heat load, and more than your 54' of baseboards could actually deliver into the rooms even at the maximum (185F) temperature setting. So whether you have it set to 30% or 100% will not make a difference in it's operation in your house- it simply can't even pump the 53K of heat into the heating loop with your radiation.

With a smart pump you might try running the Navien under return temperature control set to 125F (where it might actually hit 90% efficiency) and dribbling the radiation loop at 0.5 or 1 gpm or a big delta-T, and see if it behaves any better. The Navien is probably good for at LEAST a 50F delta-T before it's stressing it, and probably more. At 165F out, 125F back it's a 40F delta, and an AWT of 145F. With 54' of baseboard and an AWT of 145F the baseboard should be emitting ~20,000 BTU/hr into the house, but with a 125F EWT the boiler would be condensing. If the "real" design heat load at +8F is 15,000 BTU/hr, that means you would have a nearly ideal 1.35x oversizing factor, and it would still keep up well into negative single-digits.
 

Jac04

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So whether you have it set to 30% or 100% will not make a difference in it's operation in your house- it simply can't even pump the 53K of heat into the heating loop with your radiation.

So, it sounds like trying 30% might be a good idea for Mike if the flame-out problem is indeed due to over-shoot on start-up. Also, this should help promote longer burn times, right?
 

Jac04

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I am looking to find a local plumber to perform the factory recommended periodic maintenance on the unit...
What maintenance are you looking to do? Basic cleaning of the air inlet filter, DHW strainer & condensate trap is very easy, and doesn't require a plumber, only a little mechanical aptitude and a phillips head screwdriver. The manual covers the maintenance, although I have a different method for filling the trap with water - I simply fill it before putting it back in place. PM me if you want to try to do the maintenance yourself - I'd be happy to talk you through it. What town are you in? I'm just outside of Bradley Int'l Airport.
 

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Jac04: I've done the basic manual maintenance you mention, but some contractors talk of inspections of different components etc., maybe a waste of time/money? It's the flushing/descaling the heat-exchanger I am thinking about having done. The factory support rep recommended it when I said described the concerns. (Although I'd also noticed it when the unit only a few months old if not sooner). Most of the plumbers I'd talked to think it's not necessary (at least this soon even though I am on well and my water is a little hard etc). I am on well and my water is a little hard, but I checked the plastic strainer on the space heating side, and it was clean. I have a whole house filter to keep sediment out and I installed an electronic "scaleblaster" before this unit was installed- I think it has improved the water overall in the house.

Dana (and Jac04): Is the short cycling that I am seeing- extremely detrimental to the life of the unit? (or just losing efficiency)? It doesn't happen all the time - and when it does it usually only happens once per heat call, it's not continuously repeating during the same call. It does seem to run for a few minutes of burn before the flame shuts down, it's not going into a constant spiral of on and off during a single heat call, which I've seen described as a problem for others.
 

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Mike- From my memory, the manual makes no mention of specific component inspections other than the normal stuff - filter, strainers & condensate trap. If a contractor is telling you otherwise, I'd try to get a detailed breakdown of what they want to inspect. My manual actually makes no mention of descaling the DHW heat exchanger, but it is my understanding that it should be done regularly if you have hard water. Unfortunately, Navien does not specify how often or what is considered hard water (at least my manual doesn't). I have a water softener, so I'm not too worried about descaling and I'm at the 2 year mark with mine. I don't know much about the electronic 'softener' that you have, but it certainly can't hurt to descale it, especially if you feel as though DHW capacity has diminished. You should be able to buy a DIY descaling kit for less than $200 so you can do it yourself for less than the cost of having a plumber descale it.

The Navien web site also has descaling info listed under the FAQs:

I'll let Dana comment on the short-cycling, as he is much more knowledgeable than I am. I'm curious to see if he thinks that the short cycling could be eliminated by setting the max firing rate to 30%.
 
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MikeG88

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Jac04- re-reading your previously comments I probably didn't fully answer some of your questions. The fuel mixture was never adjusted on the old unit- that was Navien's next step after replacing the air pressure sensor, converting for high temp exhaust (new PC board, switch to sched 80 on the exhaust side pipe, etc), and replace the burner rod. At least three different plumbers had checked the gas pressure during operation (of course none was ever here to witness the error 12, being so intermittent). The unit had run for over a year before this problem (error 12) started, and hasn't happened with the new unit (knock on wood)- so I assume something internally changed with the gas adjustment. The adjustment was never attempted because at that point the builder told me to hold off because they had approved a replacement at their expense (or were charging back their wholesaler?). That unit had had other issues: the 3-way valve had died and we knew that was the problem because it had been making noise on and off for months (and we had a replacement on hand Navien had already sent one out), but they had the plumber check the flow sensor before authorizing the labor to replace the valve, and he couldn't get the sensor back together (the sensor was fine until that point). So I guess the builder finally realized that unit was a lemon.

I did try the old unit in return temperature mode for a while before the replace it and never experienced the error 12 problem. In return (set to 125 deg) it would fire up, supply might climb to 160 or more, and when return hit 140 (125 setting plus 15 "margin"?), which if I recall took 2-3 minutes, burner would then shut down and internal and external pumps would keep the water moving through the baseboards. Eventually as it got colder outside it would take so long that return would get back below 125 and kick on again (that's where I assume I was really losing efficiency, especially if it only had to kick back on for a short time). At this point I tried 140 degrees return- but I didn't think it was much better. If I recall from high school physics - the hotter the water the faster it cools (and even though the supply might have a chance to get well above 160, the return would drop below the 140 just as quick (or so it seemed).

One of the plumbers that had come out (Navien certified) had suggested something along the line of the smart-pump recommended by Dana. He thought this might stop the error 12 problem as he imagined it might be some extreme short cycling rather than a gas problem (but I had seen the error 12 happen on the first start up after the unit had been off for several hours and was obviously fairly cool), he had also said I needed to run supply 160 or higher to keep up without taking into consideration my LF of baseboards, etc. So I didn't go for it at the time.

As far as my understanding of the "heat capacity control": a factory tech support rep told me the regular "heat capacity control" was for the space heating side only, and "capacity of the whole" was for both DHW and space, but it would only override space if set lower than the "heat capacity control", I guess the theory being your DHW requirement will usually be equal or greater than your space requirement.

About flushing and descaling the exchanger- one of the Navien certified plumbers I talked to never does it, and the another recommends normally every two years. I haven't noticed any diminishment on the DHW etc. I just question it because a factory support rep had mentioned it when I was asking about short cycling, he was probably just following the "script" for when dealing with a homeowner. The few plumbers I have talked with about annual service- some consider the flushing or descaling an additional item- not usually needed.

It would probably help Navien's reputation if they had a manual that actually explained the settings and what/why/when and how you would use them. Along with some of the spelling and grammatical errors in the manuals (install and service as well)- I wonder if there is anything potentially dangerous- ie: a wrong number or increment quoted in the service or install manual?

Another possible solution to using up the "excess" causing the short cycling (maybe Dana has some input here also)- what about heating the basement? I've thought about it, and a couple friends have independently suggested it also. The basement is not finished (but is fairly tight- consistently about 48-50 degrees this winter, seen it drop to lower 40s past winters when we had a long cold snap with some below 0 mornings etc.) I've been considering studding out a wall to install shelves/cabinets/hang tools on, and could put some baseboard on also. Don't need to heat it to 70 down there, not trying to make it regular living space, just want to use up the "excess". Tie into same loop without an independent T-stat, just try to find a happy balance (as in how many LF of baseboard) where it uses the "excess" without increasing requirements unreasonably. (or is there another solution besides baseboards to use to heat the basement?)
 

Dana

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When it's in a short-cycling mode, how many ignition cycles PER HOUR is it doing? What are the approximate burn times during more continuous burns?

If the foundation doesn't have at least an inch of air-impermeable insulation on it (particularly on the above grade section) you can't just add an internal studwall without incurring a significant risk of being in the mold-farming biz.

IRC 2015 code minimum for foundation wall insulation for US climate zone 5A (all of CT is within zone 5A) is R15 continuous insulation, or it's performance-equivalent. If you're planning to build a studwall for ease of routing wiring, etc. the easiest/cheapest solution is to install at least 1" foil faced rigid polyiso to the concrete (seams taped with foil tape), or a minimum of 1.5" of rigid EPS, (seams taped), trapping the foam to the wall with the studwall, insulated with R13-R15 batts (unfaced preferred, kraft facers are OK, but a bigger probem if it ever floods, but no foil facers on batt.) If there is no insulation under the slab, install an 1-1.5" of rigid foam (EPS is preferable to polyiso here) as a capillary and thermal break. Cut'n'cobble rigid foam over any foundation-t0p-ledge, the foundation sill, & band-joist, with the edges sealed with can-foam, fattening up the R at the band joist with batts.

Another solution is to install 3" of polyiso to the walls, secured with 1x furring 16-24" o.c. through-screwed to the foundation with 5" masonry screws. You can hang the wallboard on the furring. This eats up less floor space, but complicates the electrical work. It can be even cheaper than a studwall solution if you use reclaimed or factory seconds polyiso, which is available from multiple outlets in southern New England. The biggest vendor is probably Nationwide Foam in Framingham, MA, but Green Insulation Group in Worcester, MA moves a lot of goods too, and there are several smaller operations. A 4' x 8' sheet of pretty-good condition reclaimed fiber faced 3" polyiso typically runs $12-20/sheet, depending on current market conditions and the cosmetic condition of the foam. Virgin-stock 3" roofing iso runs $55-65 f.o.b. the distributor's loading dock, so it's quite a discount. Do do it with EPS would take 4" to hit code-min, which gets to be more expensive & awkward on the masonry screw front.
 

Jac04

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As far as my understanding of the "heat capacity control": a factory tech support rep told me the regular "heat capacity control" was for the space heating side only, and "capacity of the whole" was for both DHW and space, but it would only override space if set lower than the "heat capacity control", I guess the theory being your DHW requirement will usually be equal or greater than your space requirement.
OK, that makes sense. Have you ever adjusted the "capacity of the whole"? Here's why I ask - this is what I saw on mine: For the longest time, I had the max heating capacity set to 30%, and the "whole" to 100% (I never tried to adjust the 'whole', I just left it alone at 100%). It wasn't until I adjusted the "whole" to lower than 100% that the 30% heating capacity adjustment seemed to 'kick in'. That's when I saw the time to reach my heating supply set point go way up. I then ended up adjusting my heat capacity to 50%, and now my ramp-up at initial fire is much more gradual, and it seems to have gotten rid of the occasional flame-out at start-up. I don't know if this is some type of glitch in the computer, all I know is what my experience is.

Not to keep harping on it, but why not try setting the heating capacity down to 30%? It's my understanding that this adjustment is designed into the unit for this exact reason - when the heating requirement is low compared to the max output of the unit. This should lengthen your burn times and still be able to keep up with the heating requirements. I would think that this should also keep the unit from over-shooting the set point enough to cause the burner to shut down.
 

MikeG88

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Dana- in answer to the question in you last post (remember I have the the basic round Honeywell T-stat set to 3 CPH) a "normal" burn lasts about 6 to 8 minutes on average. When it short cycles it will burn for several minutes, cool for a few minutes, reignite- but sometimes the call for heat end before the re-ignition, or shortly after the re-ignition. So when it happens I am getting the 3 ignitions per hour based on the T-stat's 3 CPH and another short-cycle induced ignition per cycle, for a worst case scenario of 6 ignitions per hour, based on what I have observed.

Oddly earlier tonight while running my electric dryer, I timed a burn for 10 minutes, then the burn stopped, but the call ended before re-ignition. Another time it reignited but the call ended shortly there after. The dryer is on the heated level and must be sucking a lot of heated air out of the house - the burn lasted a bit longer than average and I would have expected it to short cycle earlier than 10 minutes into the call. I have noticed this before because the bedrooms, away from the area where the dryer is, actually get warmer (you can feel it and see a degree or two increase on a thermometer).The T-stat is closer to the laundry closet. Maybe the bedrooms have more baseboard per SF than the more open living room, kitchen & dining, and laundry closet. (Or are more isolated from the areas having the heat sucked out of them).

Jac- I'll try lowering the heating capacity further when it's a little warmer and I have time to observe it over a period. Some start ups seem fairly smooth now and some involve a bit more ramping and shifting, and the occasional flame restart. (And I think sometimes you are not sure if there is a restart or just a "shift" because I think the remote controller and the green burner light on refresh only every so often).
 

Jac04

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Interesting. Since your 'normal' burn times are fairly long, I wonder what the difference is between a 'normal' burn and a 'short-cycle' burn. On a 'short-cycle' burn, it sounds like you could be losing flame for some reason, but it won't re-ignite because it hasn't reached the 15 degree delta-T below the set point telling the burner it needs to start firing again. I guess I'm thinking it could still possibly be a fuel supply issue. Could you give us a description or sketch of the piping system (pipe sizes, lengths & locations of regulator(s).

The green light on the controller does seem to lag about a second, but on mine the light would always go out if I saw a 'shift gears' flame loss.

UPDATE: I've been watching my unit for the 'shift gears' flame loss, especially since I have changed the max heat capacity to 50%. I haven't seen it for a while, but I saw it last night. I use a very small setback at night for sleeping comfort, which gives me a long time between burns right after the setback. So, when the unit fired after sitting for a while I saw the flame loss for a moment at start-up. Since the issue seems better with a lower max heat capacity, I set it down to 40% last night. I'll keep an eye on it.

It's weird that both of our units do it, but seemingly under different circumstances. It almost makes me think that there is something in the computer logic that it telling it to shut off for a moment. I quickly looked at the logic schematics for my unit, but didn't see anything that would cause it. When I get a little more time, I'll check it out more closely.
 
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MikeG88

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Jac- you may be right on the green burner light only being delayed, it's the temperature display readout on the remote that seems to only update every so many seconds. You asked about the gas system: 120 gallon tank right outside the house with regulator (twin-stage?) and pigtail to the penetration. Inside there is a straight run about 20' 7", a gentle curve and about 8' more to the unit, then it drops (gentle curve again) about 4' to the shut off. Short solid black pipe nipple to a T with the "sump" at the bottom, out the side another short nipple to an elbow to the gas input on the unit. Except for the black pipe the line is all that corrugated pipe with a black jacket - I came up with about 1 1/8" trying to measure the OD including the jacket. I actually had these measurements because Navien wanted them when I was having the start/stop/start/stop problem with the old unit. No visible kinks or dents, all curves are gentle. Navien thought this was sufficient as well as everyone who has seen it in person and tested the pressure under load.

Dana & Jac- early yesterday morning I woke up and checked my outdoor thermometer and it was 18 degrees here. I timed a couple burns pretty close to 8 minutes (with approximately 12 minutes between), and didn't witness and short cycling or momentary flame losses. (running 160 degree supply, 60% capacity, slow setting on circulator). Wondering if burn times are relative in that with a 52 degree differential (70 indoors minus 18 outdoors) would the necessary burn time increase approximately 20% if the outdoor temperature was around the 8 degree mark (10 additional degrees of differential divided by 52 degrees = 19.23%)?

I spoke with a couple area plumbers yesterday, both fairly knowledgeable with modulating-condensing boiler systems. One of them has taken some of the Navien classes, has the parts kit and has installed a lot of the NCB units. After describing the issues he's leaning toward a computerized pump also, but wants to go through a standard service call to verify no other issue causing or happening alongside this. I'll probably have him out during the week.

What I have a hard time wrapping my head around with primary and secondary loops: if you slow the flow through the secondary loop way down, won't the excess 'heat" just make it back into the unit through the primary (since it's literally a loop), or even just get "backed-up" because it has no where to go?
 

Jac04

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I hate to be the bearer of bad news, but a cursory review indicates that your gas supply system is not adequate. 3/4 CSST measures roughly 1 1/8" OD. If you go by the Rego charts, 35 feet of 3/4" CSST is only good for a capacity of 165k BTU/hr. And that's not taking into consideration any bends or other piping &/or fittings being part of the system. The capacity of your piping system will end up lower than 165k BTU/hr. Your unit needs a supply to support 175k BTU/hr. I can also tell you from personal experience that a single twin-stage regulator does not play well with the Navien. It doesn't react well to changes in load. My CH180 had all kinds of flame loss problems with a single twin-stage regulator.

Now, you also said that you have a single 120 gallon tank. You need to look at the capability of the tank to supply the fuel you need - this is called the vaporization rate, which is based on tank size, temperature and % fill. From the info I have in my files, a 100 gallon tank at 25% full can provide about 100k BTU/hr worth of fuel at +20F, well below what you need. Now, obviously the tank will provide much more fuel when full, and/or when it is warmer outside, but having a single tank is likely a secondary issue as well. FYI, I'm running dual 100 gallon tanks for my CH180, which is what the propane company said I needed at a minimum.

Anyhow, you really need to look at your propane supply system (or have it reviewed by a competent technician). Before making any changes, you can ask them for the piping sketch, equipment selections & sizing calculations so you (we) can review them. I'm actually on my 4th propane system. My original propane company & installer did the first 3 working in conjunction with a Navien rep. Turns out that they were all a bunch of hacks, making sizing decisions based on what they thought was OK. Not one of them did any calculations or looked at capacity charts. I assume the people 'looking' at your system aren't really analyzing it either. All the tests they did on the system told them that everything was OK, but it wasn't. Everyone uses a digital manometer these days, which doesn't do a very good job at showing quick transient pressure fluctuations. I made a 'real' U-tube manometer and found that supply pressure was all over the place. When I told everyone about it, they looked at me like I had lobsters coming out of my ears. They had no idea what a real manometer looked like, and a bent tube with some water in it certainly couldn't be giving them any type of useful information. What a bunch of knuckleheads.

So, I finally educated myself on the propane systems and sized up a 3-stage system, utilizing 2psi for the majority of the piping. My NEW propane company then came in and quoted the system, which ended up matching my selections.
 
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MikeG88

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Doe's my unit really need all that since I am never really using it any where near it's rated max at least for space heating? (I guess if I open all the hot water faucets the DHW cdraw could go that high)
 
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