I put most of the stuff in my summary. I am trying to find the thermo gauge or some type of thermostat on the heater itself but not sure where its located. I have the manual but that didnt do me any good.
Is the burners coming on and then shutting off. and then it starts all over again??
If it is then most likely it is the ignitor/flame sensor. Make sure the sensor is in the contact with the flame. Also if the burner has a lot of rust on it clean it off with a steel brush it acts as the conductor for the ground.
The ignitor is also the flame sensor. When burner shuts off like that, see if gas valve is still getting 24-28vac at the GV terminals.
If not, then the problem is electrical and/or safety issue.
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SOURCE: Thermostat calling for heat but furnace shuts off and on
I had to fix a similar furnace recently I cut 2 cm off the end of a hose and made it tighter I tapped the relay on the circuit board in case it arced and spot welded itself shut All worked fine right afterwards
Testimonial: "i could try shortening the tube but it seems short enough. I don't understand the second part of your solution. I've never dealt with circuit boards/furnaces before"
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yes it runs for anywhere from 2 minutes to sometimes 30 then will just stop but you can hear the hum like its about to start again, then within a minute it fires right back up and will continue to either cycle on and off a few more times or just continue running through until it reaches the set temp.
Does this have a mercury thermostat?? It might be out of level also
check the heat anticipator on the thermostat move it to run longer.Also check the condensate trap to make sure it is draining right. if is not that can cause the pressure switch to drop the burners out and then once it drains some water will make and the burners will come back on.The huming noise is most likely the transformer which is normal.
Also check your air filters and your evaporator coil to see if they are clean. The furnace could be tripping the main limit switch which is from lack of air across the heat exchanger. With out being there to see how it working it could be several things or a combination.
You will just have to check one at a time and restart the furnace to see if that was it.I know sometimes it is a long process to fix it.Good luck.
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