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Old 12-09-2011, 11:12 AM   #1
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Heater cycles off after 2 minutes, how to troubleshoot?


I have a comfortmaker(model number NBf075F16A1) gas heater that will turn on for about 2 minutes then turn off. It will continue to turn on and off every few minutes till the house has reached the desired temp.

I've read around on the web some and I think the temperature sensor may be triggering the shutoff. Does anyone know of a way to bypass the temp senor, or maybe get a new one?




I had a pro come out and take a look and he said the condenser coil was dirty and he would charge me $1200 to cut it out and clean it. After he left I took the access panel off and saw the coil was not that dirty at all. So now I'm very hesitant to have anyone else come out because I don't want to spend another $85 for bs work.
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Old 12-09-2011, 11:22 AM   #2
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Heater cycles off after 2 minutes, how to troubleshoot?


Clean the intake filter or change it.
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Old 12-09-2011, 11:46 AM   #3
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Heater cycles off after 2 minutes, how to troubleshoot?


I've recently changed it, but I guess I could try again.

I actually found a guy on the web the describes the exact problem I'm having with the same model of heater. Only if I could find a way to email him here.
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Old 12-09-2011, 12:30 PM   #4
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Heater cycles off after 2 minutes, how to troubleshoot?


what is turning off every 2 minutes...the supply fan...the burner that induced draft motor does it stay on the entire time the stat is calling the heat as it should...check the round blades on your main suply fan no dirt on them rounded off...get back and that call was a ripoff in the making if it just has dust on it no big deal....
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Old 12-09-2011, 12:39 PM   #5
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Heater cycles off after 2 minutes, how to troubleshoot?


The burners are turning off after 2 minutes, the fan and blower stay on for maybe another 1 minute and then the entire systems shuts off. After maybe another 20 seconds the process start all over again. This is what the blower looks like.



I was able to reach my hand in there and feel that the blades are ok, maybe a little dusty. How else would I inspect them?

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what is turning off every 2 minutes...the supply fan...the burner that induced draft motor does it stay on the entire time the stat is calling the heat as it should...check the round blades on your main suply fan no dirt on them rounded off...get back and that call was a ripoff in the making if it just has dust on it no big deal....
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Old 12-09-2011, 01:04 PM   #6
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Heater cycles off after 2 minutes, how to troubleshoot?


dust is OK there...check all those terminals on the control module on the fan housing for tightness especially those low voltage ones....you said the fan goes off what is the cycle of that small fan above the burner section that should sstay on as long as the stat is calling for heat...if not pull the sta off the subbase and jump over R to W for a continued heating cal...then see if that small Inducer Draft motor stays running...don't reset anything except to start this jumper test...
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Old 12-09-2011, 01:35 PM   #7
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Heater cycles off after 2 minutes, how to troubleshoot?


This sounds a lot like the problem I had last winter. Gently tap on the side of the gas valve with a screwdriver handle or something while the burners are going. If the flames "bounce" or shut off, the gas valve is shot.
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Old 12-09-2011, 01:38 PM   #8
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Heater cycles off after 2 minutes, how to troubleshoot?


I timed everything out. Turn the thermostat on heat. Burner, exhaust fan and main blower(?) turn on.

5min 30sec burners turn off (this time seems to vary) thermostat reads "Wait" after this
6min 30sec small exhaust fan turns off
8min 45sec main blower turns off

I will try crossing R to W but I'm pretty sure it is calling for heat and some sensor is triggering the burner stop.

I also noticed that where the starter flame\ignitor is there is a large flame. In the picture it is between the two burners. Is that normal?

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Old 12-09-2011, 01:42 PM   #9
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Heater cycles off after 2 minutes, how to troubleshoot?


Do you mean the gas valve that comes out of the wall with the ball joint? Or possibly the valve inside the furnace? If inside what should it look like?

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This sounds a lot like the problem I had last winter. Gently tap on the side of the gas valve with a screwdriver handle or something while the burners are going. If the flames "bounce" or shut off, the gas valve is shot.
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Old 12-09-2011, 01:45 PM   #10
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Heater cycles off after 2 minutes, how to troubleshoot?


In the picture in your first post, it's the thing on the gas pipe with the beige plastic box with a warning label on the front.
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Old 12-09-2011, 06:02 PM   #11
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Heater cycles off after 2 minutes, how to troubleshoot?


Did you look at the bottom side of the coil or the top? The bottom will be where the dirt is.

If you have a voltage meter put a lead on each of the 2 wires on that black disk behind the gas valve. If the furnace over heat the voltage showing on the meter will change from 0 to 26. That will confirm not enough air flow and a possible blocked coil.
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Old 12-09-2011, 06:11 PM   #12
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Heater cycles off after 2 minutes, how to troubleshoot?


I looked at the top of the coil, or what I think is the top. Here is basically what I saw. This isn't mine, but it looked very close to this in condition. When you say under do you mean under the metal part?

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Old 12-09-2011, 06:23 PM   #13
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Heater cycles off after 2 minutes, how to troubleshoot?


Yep....underneath that coil is where the dirt is caught....looks pretty on top.....
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Old 12-09-2011, 06:34 PM   #14
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Heater cycles off after 2 minutes, how to troubleshoot?


Correct. They can look good on the top but the bottom can be a matted mess of filth. Just be careful taking that plate off, those copper pipes are easy to poke a hole in with sharp edges of sheet metal being bent around.
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Old 12-09-2011, 06:55 PM   #15
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Heater cycles off after 2 minutes, how to troubleshoot?


I don't think I'll be able to remove the coil to clean it. It is behind the freon lines. I was able to remove the panel enough to look at it. I did find a foaming cleaner here that is meant for coils. I may try spraying that on top of the coil and see if that helps. If it was matted up and I sprayed that on the top of the coil do you think it would help? I would think it would drip between the fins and soften the matting...

On a side note I reduced the gas flow to the heater by turning the ball valve and it's been running for a good 20 minutes, longer than it has ever run. Maybe it was getting too much gas an producing too much heat?
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