Zone Trouble shooting help

[JEM_1964]

Hello all,
I am new to this forum and hope this issue is solvable and helpful to others. We are renovating a 1925 stucco colonial in Eastern Mass and had a complete HVAC system installed with a Navien combo boiler and two 3 ton air handler units with hydro coils. The system is plumbed with 1" PEX using two zones and one main pump. the downstairs zone is working perfectly but the attic handler cannot get hot water - I believe this zone is air bound.

I can shut off both zones and manually open each relay valve and feel the resistance - this resistance goes away if the thermostat is calling - so I think the zone valves themselves are fine. I have tried to bleed the line but cannot do so - or at least it is not changing the situation. I think either one of the valves needed to bleed the line is broken, or an alternative is that the pump that is asked to push the water through the system is not sized to handle the two zones.

I have checked the wiring both units work and are controlled by their respective thermostat, but one never gets warm water in its system - even near the Navien boiler unit. I have tried manually opening the upstairs zone valve relay and turning on the downstairs just to see if warm water would move through both zones but no. The original installer is not supporting us so I am looking for a strategy to at least determine what is wrong.

Any thoughts to point me in the right direction will be most appreciated.

Thanks,

Jim

 

[Stuff]

Did it ever work? If not it could be a check valve installed backwards. Could still be a bad valve. Also make sure the return pipe actually exists. Maybe the air handler isn't even connected. Since PEX it also could be a pinched line somewhere. Could be a clog in the system.

You need to find a new HVAC company that has the tools to isolate and repair the problem. Attach a pressure gauge at different points in the system to see how far the water can go on the upstairs loop and back.

 

[Sponsor]

 

[JEM_1964]

Did it ever work? If not it could be a check valve installed backwards. Could still be a bad valve. Also make sure the return pipe actually exists. Maybe the air handler isn't even connected. Since PEX it also could be a pinched line somewhere. Could be a clog in the system.

You need to find a new HVAC company that has the tools to isolate and repair the problem. Attach a pressure gauge at different points in the system to see how far the water can go on the upstairs loop and back.

First of all, thank you for taking the time to respond, I agree with you that I probably need professional help (that's in general, BTW)

The upstairs zone never worked, although water was in the lines as they froze during the winter (The plumber was not supposed put water in the lines until the electrician hooked up the air handler). The upstairs hydrocoil had to be replaced and everything works but for the fact warm water never makes it up to the 2nd floor unit. The downstairs unit works perfectly, hot water is found in both out bound and return pex lines. The upstairs unit lines do not get hot water anywhere but just at the zone valve itself. There is an in line faucet valve to bleed the lines and a valve nearer to the boiler that I am supposed to close before opening the valve to bleed the line - this is the valve I worry does not work. The downstairs lines are not air bound but if the valve I worry about is broken I think that I am actually not able to bleed either zone. The upstairs lines do not have any way to bleed air near the air handler, it is all down near the boiler end. When I perform the bleeding service, I get a short burst of hot water then it runs cold and never changes.

Both zones are fed by the same valves, the zones themselves just make a loop with the hydrocoil there are no other valves in line in either zone (and the downstairs works...). It seems like I need to know if the pump is strong enough to run both zones, or if I am air bound in the upstairs unit - the reason I can't bleed the air. Since water got up to the attic in the first place to freeze, my guess is that the pump at least once was strong enough to do the job so perhaps the valve needs to be replaced. It would be great to know for sure before cutting it out, because the plumber didn't leave much room and its all crimped copper sections, not soldered joints as I have seen in the past...

Thanks again for your response, Jim

 

[WorthFlorida]

I do not know your system but does the valve work with a solenoid? If it does check the voltage at the solenoid, usually 24v ac.

As Stuff suggest there could be a clog. Perhaps a small piece of PEX is blocking the flow at the valve. If you can drain that line near the furnace check for any debris in the water.

 

[JEM_1964]

Thank you WorthFlorida,

One of the issues is that that the furnace side has no drain or air vent - its all done back at the boiler side. The air handler in the basement is about 20 to 25 feet away from the boiler but the upstairs unit is probably 75 feet away (in terms of 1 inch Heating grade PEX length). I will check the solenoid voltage to be sure it is achieving the 24V ac. Since I cannot feel hot water in the PEX near the boiler for the upstairs zone, but I can for the downstairs maybe the zone valve is not working. I didn't have a meter to test it that way, that is why I tried to manually put the valve into the open state and bleed the line - but it didn't work. Thanks again for the direction, I will give this a try.

Jim

 

[Dana]

You need to have some sort of vent or bleeder valve close to the upstairs air handler to purge it easily, since the air lock will be near the top of the system. (Where is the bleeder valve for that loop located?) But with a discharge valve/port on the return line from that air handler you should be able to get most of the air out by opening up the port, manually opening the zone valve and filling the system (with the auto-fill) until it is running water freely without hissing or chugging.

This should have been done by the folks who installed it. Is there some reason why the installer isn't supporting you here?

 

[JEM_1964]

You need to have some sort of vent or bleeder valve close to the upstairs air handler to purge it easily, since the air lock will be near the top of the system. (Where is the bleeder valve for that loop located?) But with a discharge valve/port on the return line from that air handler you should be able to get most of the air out by opening up the port, manually opening the zone valve and filling the system (with the auto-fill) until it is running water freely without hissing or chugging.

This should have been done by the folks who installed it. Is there some reason why the installer isn't supporting you here?

Hi Dana,

Thank you for your post. There is no bleeder valve in the attic, only in the return near the boiler for both zone valves. The situation as to how we got here is complicated but essentially I hired a plumber because he had certification as an HVAC installer and by getting both jobs under one contract the price was more favorable. The plumber installed the indirect hot water tank, the navien boiler, zone valves and pumps and 1" PEX for hvac but then would not honor his quote for the hvac equipment install (the price went up 70%), he also did not do the rough plumbing he had a deposit for and so I had to fire him. The HVAC company that installed our air handlers and duct work do not do plumbing, the new plumber does not like the original plumbers work and so I am in the middle trying to see how far away from working the install really is. One zone works fine, but it is less than 30 feet away, the attic air handler is probably 75 feet away. The process I have been trying to use to bleed the air was to close a check valve (which I am worried is actually broken) with the upstairs zone shut off. I then manually open the zone valve for the upstairs and open the discharge valve and let the water run. I have let it run for 15 minutes but it just runs cold water. In the boiler area, I can feel hot water in the copper pipe below the 2nd zone valve but never is there warm water in the PEX going to or coming from the attic but the working zone has hot water in both lines. I can believe the zone valve is broken but the resistance is there when I open the valve manually - I still have to verify the 24v control is getting there. I also tried opening the second zone valve manually and using the first zone thermostat to call for hot water so that both would get warm water but no hot water was in the second zone lines - if manually opening the valve was working then the second zone is still air bound I am guessing...
I really appreciate your help, can you explain the auto fill process so I can check my steps? One thing I worry about is emptying the Navien boiler of hot water and dumping cold water in too quickly.

 

[Dana]

Vertical feet is more important than horizontal feet. Air is lighter than water, and will congregate at the highest elevation if allowed to, and that's why most competent hydronic contractors will install an air bleeder valve (or even a vent) at or near the top of the system. While it's possible to purge air working from the bottom of the system, it's a PITA, and the physics is working against you, not for you.

An auto-fill valve is just a convenience device where you fill the system to keep from overpressurizing the system while filling. It doesn't have anything to do with purging air other than it will keep filling the system as you are draining water/air from some other part of the system.

If there are any threaded fittings (say a union) in the system plumbing near the upstairs air handler you can crack it open to bleed some air, or at least verify that water has made it that far up in elevation. If you back off a threaded fitting and there isn't even a hint of a hiss or a dribble, there is probably some isolation valves closed in the system keeping water from flowing on that loop.

I'm not quite clear what you mean by " close a check valve (which I am worried is actually broken) with the upstairs zone shut off ". Check valves are not usually manually operable devices. You need all valves to the upstairs zone to remain open in order to purge air, but if there are ball valves or gate valves to isolate the indirect or the other zone while you're filling & purging the upstairs zone that can be a good thing, since it means you won't accidentally inject air into the first zone. Air purging is best done with power to the boiler off so that it won't fire up while purging is in progress, potentially delivering scalding water at your drain point.

 

[Dana]

BTW: An air handler & heating ducts in an unconditioned attic above the insulation in a MA climate is already a big mistake, and a HYRONIC air handler makes it even worse. You've already discovered the freeze-damage problem with putting a hydronic air handler in the attic without benefit of antifreeze in the system (which would have it's own set of issues.) With the air handler & ducts in the attic the supply to return duct balance needs to be perfect, and they need to be sealed perfectly (along with the penetrations at the ceiling for the ducts & registers, and anything else) to prevent air-handler driven air infiltration, which can be a significant fraction of the load. Ideally it would all be inside both the pressure and insulation boundary of the house, which makes it much more tolerant of duct leakage. Balancing the ducts and air sealing the house also reduces the fraction of the air that uses the great outdoors as the path of least resistance. Putting it up in the attic is the worst of all worlds, but (sadly) often done as a means of retrofitting air conditioning.

A pair of 3 tonners is also a breathtaking exercise in oversizing for the loads too, unless this is a practically uninsulated 4000' house or larger. A typical 1920s house with some retrofit air sealing, some wall insulation and at least some storm windows over antique wooden double-hungs in eastern MA will have a design heat load of about 15 BTU/hr per square foot of conditioned space, to maybe 20 BTU/hr per foot if there is no foundation insulation and lot of air leakage. If you have 72,000 BTU/hr of air handler that's either a pretty big house, or significant oversizing (which is pretty common for gas furnaces, but unforgivable for new hydro-air.)

Can you share the model numbers of the air handlers?

For reference, my ~2400' circa 1923 bungalow in Worcester comes in at about 35,000 BTU/hr @ +5F, but was on the order of 50,000 BTU/hr @ +5F before squirting some cellulose into the walls, insulating the foundation to IRC 2015 code-min, and a round of air sealing (including un-venting the attic spaces behind the kneewalls and putting ~R20 foam on the underside of the roof deck in those areas.) This is no super-insulated gem by any means, with ~R18-R20 in the attic, clear glass storms over the antique windows, no insulation around the exterior wall chimney, etc. At the water temps I'm running I'm radiation-limited to ~45,000 BTU/hr out (about 1.3x oversizing) and it doesn't lose ground even at -10F outside.

 

[JEM_1964]

Hi Dana, I will indeed. We did a complete remodel and the attic was reframed and insulated with spray foam insulation. There are 4 floors in total, a basement and first floor as one zone (which works but will lose ground when it is very cold outside by itself) and a second floor and attic as the second zone. The equipment was originally going to be unico when we installed the Navien boiler and the domestic hot water infrastructure, but the hydro air units became Hi-Velocity systems when we changed installers. The total square footage is probably 3500 because I do not heat the undercarriage garages. Hi-Velocity systems were one of the first hydro air manufacturers from Canada - as far as I can tell the machines work great when you can get hot water to them - but I have not tried the AC side yet as the condensers are not powered up yet. I will take some pictures as well so you can see the layout properly - I really appreciate your thoughts on this matter as I am with everyone who has helped so far!
Best regards
Jim

 

[Dana]

Four floors in total?

If the boiler is in the basement and the air handler is in the conditioned attic making it effectively a story difference you could be looking at ~40' of elevation gain between the boiler and the air handler, it will require system pressure (measured at the boiler) of ~20 psi for the system water to even reach the upper air handler with sufficient pressure remain positive relative to the attic's atmospheric pressure on the return side of the air handler plumbing. At too low of a pressure it will suck in air! At a ~40' elevation difference it needs at least ~17-18 psi (measured at the boiler) to even fill the system to the top. Most systems in 2 story houses are set to 12-15 psi, which is usually fine, since the top of the system is at most few feet above the floor of the second story, but in your house it's at least a few feet above the CEILING of the second story.

What is the actual vertical distance between the boiler & upper air handler?

What is the system pressure?

Which series of Hi Velocity (they may several), and/or the model number?

Tell me more about the attic insulation (location & density of the foam, thickness, etc.)

 

[JEM_1964]

Hi Dana, The top image is the boiler room setup in the basement, the two zone valves are located in the far left hand side of the picture. The blue handled bleeder valve is the middle with a garden hose attached, and the horizontal yellow handled ball valve is the one I suspect is broken, that I am supposed to close to try and bleed the air out of the system. I hadn't seen your last thread when I got this information, but it is absolutely true that the attic air handler is on the fourth floor, at least 25 - 30 feet vertically above the mechanical closet where the picture you see is located. The navien boiler combo I believe has a diagnostic mode that will report water pressure and I will check that tonight.
The insulation is closed cell spray foam in the attic, but the two by 4 original exterior walls on the first and second floors are regular insulation as the house is a renovation and not a total new construction. We are using 1" PEX to carry the water and the total length of travel is probably 40 feet in one direction. In the mechanical closet where the return just comes into the room, the PEX is cool to the touch where the same line for the downstairs zone is warm / hot to the touch. The copper pipe below the two zone valves is extremely hot and the right hand zone valve has hot water when calling, while the left hand (the upstairs zone) is never more than slightly warm right at the valve. However, I can open this valve manually and feel the resistance. The green pump in the center of the picture (Taco product) I believe supports both zones. I know there is water in the lines so hopefully the pump is sized properly. Thank you again for your assistance with this! The second picture is the model number of the air handler, they both have hydro coils for heat and another module for AC but this is not yet in use... Best regards, Jim

 

[JEM_1964]

Hi Dana, To be clear, the attic is finished with a closet for the Hi-Velocity equipment. It sits on the floor of the attic space but over the front of the house where the mechanical closet is on the back of the house half way between the floor of the basement the first floor so lets say it is two and 1/2 stories vertically separated...

 

[Dana]

Each HE-Z-70 is good for 37,400 BTU/hr at an entering water temperature of 120F, which is enough to heat my whole house(!), and you have two of them? At an EWT of 130F (still good for condensing, with a return temp of ~120F or lower) a single one of these could probably heat your whole house too.

How much closed cell foam?

The vertical distance measured in feet or meters, from where the system pressure is being measured and the top coil (or at least the plumbing taps for the coils) in the air handler defines the minimum temperature. There is no well defined distance per story it could be 9 feet or it could be 15 feet.

If the top of the system is 30' above the pressure measuring point it takes 13 psi to just bare fill the system, and 16 psi to have a reasonable margin for running the thing without it sucking in more air. Auto-fill valves often come pre-set to 12 psi, which is not enough to fill the system, if that's the distance. Knowing the vertical distance to within a foot or so is important for figuring this stuff out, but that's a prime suspect of why you are unable to purge the air out of that zone. Figure on 0.433 psi per foot of elevation to fill, add an other 3 psi to keep it from sucking air while pumping.

I don't see where the potable water is fed into the system in that picture.

Aut0-fill valves for filling the system are adjustable, and limit the pressure of the fill water to a lower pressure than the potable line pressure, which is quite a bit higher than you need or want for most heating systems. There are variations on the theme, but they look generally like this:

In MA they will also have a check valve to keep system water from backfeeding into the potable plumbing.

Find the model number on yours, and look up the instructions on how to adjust it online, if you can't figure it out by looking at it. Hopefully there is a temperature gauge nearby where you can eyeball it while adjusting it. (Can your Navien display system pressure?)

 

[JEM_1964]

The Navien combo boiler NCB-E150 is the model number and it does report water pressure and temperature and a lot of other data points. Perhaps once air got in the system - the available pressure is not able to over come the required force to purge it. Especially since there is no bleeder valve up there! The basement living space will some day be rented and so having two zones was the thought process - if you think I could have saved half the money going with a single unit or even a larger single unit I am saddened by that news but at this point just getting the system working as it should will be enough. I will look for the proper valve, get its adjustment settings and read how to display water temp and pressure to see whats up. Thank you so much for all your help with this. It makes a lot more sense to me why the lower zone works and the upper does not when all the equipment is essentially the same...
Thanks and best regards

Jim

 

[Dana]

Zoning floor by floor isn't insane (it's really the right thing to do!), but even a pair of HE-Z-50 s would have already been sufficient overkill, and would cover the likely zone loads even with 110F water. Going bigger doesn't buy you anything. The 1" PEX and that Taco 011(?) pump also seem like extreme overkill, even for the HE-Z-070.

If it's a fixed speed Taco-011 it's probably worth replacing it with an ECM drive smart pump to cut the truly excessive pumping power, but that can wait until you've debugged the functional issues, and can take some basic measurements with both air handlers running. With just one air handler running there's probably less than a 5F temperature difference between the incoming and return water at the air handlers with that monster pump in place, even with the air handler running at it's maximum speed. Ideally it would be at least a 10F difference at min-speed on the air handler, even with 120F output on the boiler. With a smart pump programmed to control the pump based on temperature difference it's possible to get there at any water temp & air handler speed, but the correct sizing may take some calculating &/or measuring. If the existing pump is the variable speed Taco-011VRF4 version it might be workable, but I doubt it's ideal. The pumping head of most air handler coils just isn't that high.

 

[JEM_1964]

Hi Dana,

The taco unit on the left is a 013-F3 circulator unit. The specifications I read on the unit said Max Head 32 ft. Is this the maximum vertical height it can be asked to push water?
Copied from spec sheet
Performance Data
Max. Flow: 33 GPM
***Max. Head: 32 Feet
Min. Fluid Temperature: 40˚F (4˚C)
Max. Fluid Temperature: 230°F (110˚C)
Max. Working Pressure: 150 psi Connection Sizes: 3/4”, 1”, 1-1/4”, 1-1/2” Flanged

The green pump on the right is a Taco Viridian Delta-T Variable Speed, ECM High-Efficiency Circulator it is set to max in the picture below. The copper piping on the right comes from the returns of the HVAC water lines. I found a data sheet on line for one model, I am not certain it is mine - but the air purge has a sequence and I wonder if there is a sequence I need to go through as well.

The valve on the right hand side of the picture below, behind the blue tag and above the green expansion tank has a sticker that calls it a spirovent microbubble resorber. I am having trouble finding the auto fil valve if this is not it. I do think it has to do with purging air from the system but I
think it has more to do with air from the water itself in an operating system over time. I think purging air out of the system is a separate function.

I am wondering if the taco circulator is sized correctly for the attic run. The microbubble resorber looks the most like your auto fil valve picture but is it possible for the Navien combi unit to have this internally? Here is a picture of the top of the unit just in case.

I appreciate your patience, I hope these pictures are helpful.

Best regards

Jim

 

[Dana]

You don't need the pump to fill the system, though if it were drawing from water at atmospheric pressure yes, 32' would be where it stalls and can't push any higher. The pumping head is the friction equivalent of the all the plumbing and hydro coil presents at some specified flow rate, and the pressure at the pump's input has the full height of water in the pluming bearing on it anyway, so the pump really only needs to make up the difference at the needed flow rate. There are standardized calculations by which the hydronic designer can determine the head-friction of the plumbing, and the pumping head of the coil in the air handler at different flow rates is also usually specified somewhere in the documentation.

That monster 013-F3 appears to be driving the primary loop through the Navien, and not out to the zone plumbing? Is it pumping directly into the return side of the boiler? (The thing comes with it's own internal primary side pump, and shouldn't need an exterior pump unless they're doing something really weird!) Can you take the cover off, and get a shot of how that big pump is plumbed into the boiler? Did they even pull the internal pump? This looks like a hack on a kludge fix to some problem real or imagined.

Take a look at the fairly clean installation NCB boiler installation in this video, which like 99% of systems out there uses the internal pump for the primary and a couple of high-efficiency zone pumps for the secondary loops. A single smart pump + zone valves is also fine- the highly efficient ECM drive Viridian is probably the pump serving the air handlers.

The spirovent continuously purges air to prevent air locks developing once flow has been established, but can't contribute to the intial purge/fill of the system unless it is plumbed in near the highest elevation on the system.

The auto-fill valve is the thing with the blue tag on it, that has the flip-lever and has an adjustment screw. The tag tells you the model name and the pre-set pressure it was set to at the factory, and it's adjustment range:

Note, the one in the picture was pre-set to 15 psi, which is fine for most systems, but may not be high enough for yours, due to the higher than average vertical distance between the fill-valve and your upstairs air handler. See the short-sheet installation guide for how to adjust it. You really need to take careful measurements and come up with the vertical distance, not a WAG. You can install a temporary pressure gauge onto the hose connection you have been using for purging the system. (Box stores often have pressure gauges designed for 3/4" hose connections- try to get something with a max of 100 psi or less for this job- under 50 psi would be even better.)

If there isn't anything supporting the expansion tank, the moment-arm of the horizontal plumbing stub on which it is attached could eventually be a leak issue but it's pretty short. It would be better if it were on the input side of the circulation pump than on the output side, but the bigger pump cavitation problem is on that humongous 013 pump anyway.

 

[Stuff]

Check the model number but that Taco Viridian may have a max shutoff head of 18'

 

[Dana]

Based on the knob setting in the picture according to the manual the Viridian is set up to run in fixed speed mode, set to the maximum speed, which is again probably overkill. With zone valves and 2 zones it's more common to set it up in constant pressure mode, so that it pumps harder when both zones are calling for heat.

The fact that it stalls to effectively zero gpm at 18 feet of head pressure has no bearing on the elevation difference between the pump and the air handler, since the input and output side of the pump are at essentially the same elevation, same pressure. The only head that the pump can sense is the difference in pressure between it's input and output sides, which is a function of the flow rate & plumbing friction (including the air handler coil).