Navien CH210ASME- burner cuts out for an instant

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Jac04

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Mike-
You still around? Thought I would give an update on a possible solution to the original issue, which was momentary flame-outs on your CH-210 ASME.

I have a CH-180 ASME, and I would get a momentary loss of flame occasionally - usually when the unit is ramping up. I limited the firing rate to 30%, which I thought helped a little, but I have still seen the issue since, so that wasn't the issue.

So, last time I was inside the unit cleaning the intake screen, I looked at the connections. These CH units were apparently known for having bad grounds, so I had already scraped the paint away from the main ground connection to the case. But, as I was looking inside, I noticed another ground connection, and followed it back to the flame detector rod. I cleaned the paint off the case at that connection and I haven't had the loss of flame problem since doing so.
 

MikeG88

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Hi Jac,
I just took a look in here for the first time in months and noticed your new post. Do you have any pictures of the connections you "cleaned", it sounds like something I can safely check/try myself. I still occasionally notice the momentary flame out that seems to happen when ramping up.

Another issue probably not related -when we had the warm spell a few weeks back I noticed it short cycling after the burner was on for maybe 6 minutes or so. I tried lowering the supply temperature, but that would increase the burn time required and give the water in the system more time to become saturated with heat and still short cycle. I was wondering if I changed my thermostat CPH setting from 3CPH (what "they" recommend for the higher efficiency systems) to 5 CPH (recommended for the no so high efficiency boilers). My theory being that 5 shorter burns in an hour with no cycling during the burn is probably better for the unit that 3 longer burns with cycling during the burn (although it wasnt short cycling during each burn). I know it a condensing boiler- but I don't have enough baseboard to run a nice long continuous burn, and my gas bill isn't bad at all (although lower is always better- it's still a drop in the bucket). I am more concerned with keeping it running (longevity-wear and tear) than saving a few dollars in gas)

Also I have noticed: that my water pressure on the readout has dropped over time. Months ago after a burn and purge it would settle at 16psi and maybe drop over a long period of time (hours) to to 15 point something. Now once the burn and purge cycle is done it settles at 14.5psi and will drop to 13.8 after several minutes and several degrees additional cooling. I called Navien tech support and they said it may be nothing or I may have lost some pressure through micro-leaks (described as leak you cannot really find because they evaporate quicker than any moisture can accumulate). They also pointed out that auto-fill will kick in when/if pressure ever dropped to 7 and change, and will shoot for 12psi (unless the setting has been increased through the controller pad) which they consider ideal, but unit should still run fine below 12 but above the 7 and change point. When the unit is running it still settles in around 21psi and will vary a notch higher or lower.
 

Jac04

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If you take the cover off you will see 2 green wires attached to the back panel of the case with screws. Those are the grounds. They are a PITA to get to. With that said, I did notice a flame interruption both last night and this morning, so I guess it didn't fix the problem. As best I can tell, I get a momentary flame-out on ramp-up for heat, but ONLY when the set point is about 25F above the existing water temperature.
EXAMPLE 1:
Last night the set point was 120F. When the unit fired on a call for heat, the actual water temp was 88F and I experienced the momentary flame-out on ramp-up.
EXAMPLE 2:
I had my supply set to 120F all last night and I lost a few degrees. With the actual supply temp reading 122F and the unit firing at low modulation, I bumped the supply to 150F to heat things up quickly. It started to ramp-up and continued to fire for about 10 seconds, then the green light went out for about 5-7 seconds, then came back on.

As far as short-cycling goes, I forgot, do you have your firing rate limited? If not, lower your maximum firing rate. That will increase your burn times. The problem is that the unit will fire as hard as it can to achieve your set point, and the unit is way oversized from a heat input standpoint. If you don't have enough baseboard, once it hits the set point it can't modulate low enough to keep it from overshooting, so it shuts off the burner. I have my max firing rate for heat set to 30% right now. I don't think you want to change your thermostat - I think that may make the problem worse as I believe it will 'tighten up' the temperature range.

Now, funny you should mention losing system pressure. I always seem to lose about 1 to 1.5psi a year, which I usually notice at the start of the heating season. I keep the water supply line to the auto fill shut off, but the auto fill has never engaged (because the water pressure have never dipped to 7psi). I usually keep mine set to 11.6 to 12.3psi cold. The system is strange because it seems to display pressure in 0.7psi increments - don't know why. Anyhow, I usually notice it is down to 10.9 psi at the start of the season. So, I just adjust the pressure back up to 11.6 to 12.3psi and it is fine until the next year. I have no idea why it does this. I have no leaks that I can find.
 

MikeG88

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IIRC a Navien rep told me the the momentary flame out (at least some of the time, and opposed to actual short cycling or the 2 second on off on off problem) was because the unit couldn't "modulate down fast enough" so that kind jives with your theory.

I do have the max firing rate reduced, even though Navien will tell you that and/or lowering the supply temperature will not help short cycling, that want to blame it on the amount of baseboard or anything but their product.

Same with the system pressure, they said I could be losing pressure gradually through micro-leaks, which is possible but my bet is the unit somehow. I have looked inside and check all the relief valves etc, but find nothing. I bet the 0.7psi increments translate to some other unit used in Asia and/or Europe. How do you adjust the pressure back up?
 

Jac04

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How do you adjust the pressure back up?
I have a valve in the water line going to the auto-feed on the unit. I close that valve, then bump up the pressure set point on the unit to something like 25psi. This will cause the auto-feed valve in the unit to open, but nothing will happen because the external valve is still closed. I then carefully & slowly open the external valve until I get the pressure I want (as displayed on the front of the unit), then shut it. Then go back to the controller and set the system pressure back to 12 psi.
 

MikeG88

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Sounds like you have to be a bit careful using that method, I might not want to try that in the middle of heating season. I have tried bumping it up a few psi on the controller over what the unit display was showing (and my filler valve is kept open) but there was no reaction. So I set it back to 12. Maybe it was a big enough difference? To be sure we are talking about the same setting: it's called "the supply water pressure setting" in the operation manual? I assume that is what you are referencing. I know if the unit losses water (inadvertently left a valve open a little when checking filters, or changes to the loop etc) and it goes below the 7 point something minimum- it will re-pressurize when you plug it back in, but I would think doing something that on purpose may introduce air if you are not careful?

A Navien rep told me it should run fine below the "target" 12 PSI and when the auto-fill kicks in at 7 point something. But it does bother me to see the gradual drop and find no leaks. I would suspect the unit of slowly losing pressure somewhere.

Now this may be my most rookie question to date: what exactly does the water pressure do, especially when the unit isn't heating? (I know in iron boilers that literally run closer to boiling temperatures it does allow higher temps without turning to steam, but not sure what that does with these units made for 185 max, and again when at rest does the pressure serve any purpose?
 

Jac04

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^Yes, it's the supply water pressure setting. There really isn't any way for it to get air in the system unless the water supply line somehow gets air in it. I've always been told to keep the line to the auto-feed closed. Imagine if your system springs a leak when nobody is home. The unit will fall below 7psi, and it will keep trying to refill, flooding your house.

You need system pressure at rest to ensure the system is full of water. It takes pressure to raise water from where the boiler is up to the highest point. The experts here know the details better than I do and can explain it better, but you need enough pressure to push the water up to the top of the system and then some additional pressure to ensure the system is above atmospheric pressure at the top.
 

Dana

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That would have to be one heluva leak for it to actually flood the house! Most heating system leaks are dribbles, not gushers, but it doesn't hurt to play it safe.
 

Jadnashua

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The pressure in the system is more to prevent cavitation and manage the boiling point. Keep in mind that in an unpressurized system, from the effect of gravity, you'll see 0.43# decrease in pressure in the column of water as you go up...there needs to be enough in the basement so that there is still pressure at the highest point. In a closed system, once you get the air out, it's as much the water falling down on the return side as pushing it up on the hot side that makes it go around...the hotter water will naturally want to rise and the cold will fall, so if it weren't for the horizontal runs and various other restrictions, the system would transfer heat without a pump...maybe not as much as you need, but it could work. In a practical world, it generally needs a pump, and the pump needs enough system pressure so that it can't create a vacuum on the suction side (which can lower the boiling point way below the 'normal' 212-degrees F) to safely work. Given enough vacuum, you can boil water way below room temperature.
 

MikeG88

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Hey Jac- I'm with you on worrying about everything. I had Mitsubishi Mini-split air conditioning installed during the summer and I made sure that they could produce enough heat to get me by in a pinch if the Navien gave out. I used them to heat in the fall and my electric bill was still quite reasonable. I stopped using them because I only have two zones and the rooms farthest away would get cold if I kept the doors closed 24/7 (due to a new pet in the house). In cooling mode the difference between rooms didnt seem so great, and of course if I keep the doors open the difference isn't really noticeable (could always swap the door slabs for ones with louvers).
 

MikeG88

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Yesterday I noticed my three year old Navien CH201ASME go through the same 2 second on- 2 second off at start up like the old unit did. It didn't reach 20 times and error out with a code 12, but it did do it again on the next call (maybe not as many times), but haven't noticed it since. I just had the space heating and DHW flushed, filters checked and cleaned, propane pressure verified etc. and all was fine (I found an area plumber that is both Navien and Mitsubish certified - nice as I also have a Mitsu mini-split system). I had him back and he called tech support- they verified dip switch settings and a couple other items, but their opinion was that it's probably normal operation especially since its's running and no there was no shut down and error code. Maybe it was just a fluke, but if it seems to continue I'll try to catch it on video.
 
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