Heater Not Working in "Auto" Pics Attached

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prosedsp

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Hello, this is my first post on the forum. I have been having issues with my heating system not working when set in the "auto" position.

Background: My heating system is completely independent of my cooling system. My house uses evaporative cooling which is controlled through another wall unit. My thermostat only controls my heating.

History: As far as I know, my unit uses hot water from my water heater to heat the air in the furnace up. A few weeks ago the heater was working fine. I started to notice that in "auto" mode the heater would turn on and off rapidly out of the blue. I could tell due to the fact that I could hear the fan kick on and off rapidly (3-4 times every 10 seconds), finally it stopped turing on altogether.

I thought it might be the thermostat, so I replaced it. This seemed to do the job for a few days. The heater was once again working in "auto" mode. By "working" I mean I could hear the fan kick on and the air coming out of the vents was warm. Last night it stopped working, which means that in "auto" mode the fan no longer turns on, let alone any warm air coming out of the vents. I do hear a "click" from the wall unit when the thermostat kicks on. When I set the thermostat to "On" the fan kicks on, but no warm air comes out.

On the back of the thermostat unit, I have the switch set to "gas or oil", as this setting has been what it was set to when I bought the house. When I switch it to "electric or heat pump" the unit turns the fan on in "auto" but no warm air comes out.

Conclusion: I have no idea what is going on :) I have attached pics below for reference and any help would be greatly appreciated. I am hoping to do the repairs myself since I have found that fixing this stuff is quite rewarding!
 

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prosedsp

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More pics:
 

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prosedsp

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last pic of the thermostat:
 

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Reach4

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In the furnace, look higher. There are going to be two temperature controlled switches. One turns off the fuel, I think, if things get too hot. The other controls the fan. That normal control would usually, at least in my limited experience, have a setting to determine at what temperature the fan would go on.

I would measure the voltage on the contacts of this device if you can. If it reads about 24 VAC, then try shorting those two contacts. If the blower then goes on, I expect that unit has failed. If you don't see about 24 VAC, then the problem would be something else. Anyway, you could add a picture of that device.

I am not a pro. I have only probed a few gas furnaces.
 

prosedsp

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Thanks for the reply, I will take a look when I get home, although I do not remember seeing any other switches in the unit, just the ones in my photo. Also, since my unit uses hot water from the water heater via a pump inside the furnace there shouldn't be a control for the "fuel" should there? I am a total noob so my questions aren't based in any reality whatsoever :)
 

prosedsp

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I believe my system is a "hydronic furnace", since it uses water from the water heater that is pumped through coils that air passes over. Is this correct?
 

Dana

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Yup, it's a hydronic coil in an air handler, fed by the hot water from the water heater, and NOT a furnace.

The fact that swapping the T-stat seemed to cure it for a few days may indicate faulty thermostat wiring- when you wiggled wires installing the new one it got a better but still imperfect connection. But it could be something else, and that was just a fluke.

The way these things usually work is the wall thermostat turns on the pump (the white cylinder labeled Grundfos in the picture is the pump) via a relay, and an aquastat on the plumbing to or from the heating coil inside turns on when it senses water above 115F or so. If the pump relay or pump isn't working consistently, or if the aquastat on the coil plumbing isn't up to snuff, it could have an intermittent short-cycling sort of behavior.

Start by turning up the T-stat a couple of degrees above the current room temp to be sure it's calling for heat, then go see if the pump is running, which you should be able to feel. If it isn't, the problem is either in the relay or the wiring between the thermostat and relay.

If it's running and sounds fine, it could either be a corroded or broken impeller on the pump putting out insufficient flow, or a flaky aquastat, or a flaky contactor/relay between the aquastat and blower motor, or a bad starter capacitor on the blower motor. (Can you turn the blower on by simply turning it to "ON" with the thermostat?)

Don't do any voltage readings with the meter set to less than 120 VAC (not 24V) or you could toast the meter. A lot of dumb controls in these things will have line-voltage on them.

Try searching the web for schematics of the air handler model- a schematic would be more useful than trying to figure out how it's wired from a bunch of phone pics.
 

prosedsp

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Yup, it's a hydronic coil in an air handler, fed by the hot water from the water heater, and NOT a furnace.

The fact that swapping the T-stat seemed to cure it for a few days may indicate faulty thermostat wiring- when you wiggled wires installing the new one it got a better but still imperfect connection. But it could be something else, and that was just a fluke.

The way these things usually work is the wall thermostat turns on the pump (the white cylinder labeled Grundfos in the picture is the pump) via a relay, and an aquastat on the plumbing to or from the heating coil inside turns on when it senses water above 115F or so. If the pump relay or pump isn't working consistently, or if the aquastat on the coil plumbing isn't up to snuff, it could have an intermittent short-cycling sort of behavior.

Start by turning up the T-stat a couple of degrees above the current room temp to be sure it's calling for heat, then go see if the pump is running, which you should be able to feel. If it isn't, the problem is either in the relay or the wiring between the thermostat and relay.

If it's running and sounds fine, it could either be a corroded or broken impeller on the pump putting out insufficient flow, or a flaky aquastat, or a flaky contactor/relay between the aquastat and blower motor, or a bad starter capacitor on the blower motor. (Can you turn the blower on by simply turning it to "ON" with the thermostat?)

Don't do any voltage readings with the meter set to less than 120 VAC (not 24V) or you could toast the meter. A lot of dumb controls in these things will have line-voltage on them.

Try searching the web for schematics of the air handler model- a schematic would be more useful than trying to figure out how it's wired from a bunch of phone pics.

Thanks Dana. I am hoping that it is a loose wire on the thermostat! Also, I can turn on the blower by turning the thermostat to "on", if that tells you anything. Thanks!
 

Jadnashua

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The fan control working when you switch it to "ON" tells you that the fan is still working, but it does not tell you if they air handler circuitry is working. As noted already, when in "AUTO", the fan typically only comes on once it senses some heat. While it is possible the system might turn the fan on at the same time as the pump, only the wiring diagram will tell for sure (or being smart enough to figure it out by probing...not recommended unless you are qualified!).

So, check that the water heater is actually hot, then while it should be running, check if the pump is running. If the pump is running and the WH is hot, but the pipes aren't getting hot in there, you may have a leak and there's air trapped, preventing the pump from pushing the hot water. Is there a water pressure gauge anywhere in there? IF so, what does it read?
 

prosedsp

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The fan control working when you switch it to "ON" tells you that the fan is still working, but it does not tell you if they air handler circuitry is working. As noted already, when in "AUTO", the fan typically only comes on once it senses some heat. While it is possible the system might turn the fan on at the same time as the pump, only the wiring diagram will tell for sure (or being smart enough to figure it out by probing...not recommended unless you are qualified!).

So, check that the water heater is actually hot, then while it should be running, check if the pump is running. If the pump is running and the WH is hot, but the pipes aren't getting hot in there, you may have a leak and there's air trapped, preventing the pump from pushing the hot water. Is there a water pressure gauge anywhere in there? IF so, what does it read?

Thanks Jim! Unfortunately I do not have the wiring diagram, and I can't find it online anywhere. There is not a pressure gauge hooked up in there either :(

I will check it out tonight and report back with my findings. Thanks for all your help!
 

Jadnashua

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Most things like an air handler, furnaces, boilers, etc., have a wiring diagram in them when new...often glued to the inside of the cover, but sometimes just tucked in there somewhere, and those get lost. Look closely on the removable covers and inside walls, you may be lucky and find a diagram.
 

Dana

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So, it's not the blower motor caps.

Is the pump running evenly when there's a call for heat, and do the pipes to/from the coil get hot?
 

prosedsp

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OK, so I fixed it! It appears that I didn't take my own advice and double check all the connections that well... Turned out to be a faulty connector on the white wire coming out of the pump motor. As per Dana's suggestion I turned on the heater and noticed the pump was not running. After disconnecting and re-connecting the leads I had it turn on momentarily once I re-connected the white lead. Bought a new connector and it spun up immediately!

Thanks so much for everyone's help, I really appreciate all your info and feedback! I wish I had a more interesting fix-it story for you all, but sometimes the easiest fixes can still be rewarding ;)

Have a great weekend everyone!
 
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