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BillyHvac, Journeyman HVAC Tech
Category: HVAC
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Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a Janitrol GMP075-3 furnace that will not light. I

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I have a Janitrol GMP075-3 furnace that will not light. I have tried cycling the power and gas valve and nothing seems to work. The ignition element is lighting but that is all. It seems it is likely the gas valve, but can I check this? My gas valve is a B12826-14.



Hello, are you familiar with what and where the pressure switch is ?

Customer: replied 6 years ago.

I am not completely familiar, but I see a device hooked to the blower by tubing with some electrical terminals.


The rest of the components are in the lower section behind a cover/

Customer: replied 6 years ago.
yes, i see it


we want to identify if the fault is in the proving section of air flow. Turn the power off.


Remove the 2 wires from the switch, start the furnace, after the exhaust fan starts touch the 2 wires together so they make contact. Hold them that way. Tell me unit progresses or not.

Customer: replied 6 years ago.
The unit does not progress with the switch jumped out

Thank you,


put wires back. Now around the burner box are dime sized switches with tiny reset button in the center. See here -


Press center button on all the switches around the burner...tell me if one clicks.

Customer: replied 6 years ago.

Do I need the power on before hitting the resets?

Customer: replied 6 years ago.

How many resets should I find? I see something outboard the circuit board that looks like a reset, but nothing on the board that I can identify.

Follow the purple wire from the gas valve. It will lead through a series of 4 resets
Customer: replied 6 years ago.
I found all the resets and the unit now works!!!!!!!


Excellent!, here is the deal...If the reset pops again we have to find out why. The safety can pop if the vent was plugged a bit...or if the heat exchanger has a crack.


The thing to do is watch the flame as it starts, watch the pattern and when the blower kicks on see if the flame flutters at all. That would be the sign of a blocked or cracked exchanger.


I thank you for your patience, it was nice working with you.

Customer: replied 6 years ago.
You are correct. The unit has cut off again. I will have to have someone look at this more closely. Your help has been valuable.


Sorry, wish you had heat. The great thing about that furnace can only be cold if something goes wrong. It is loaded with safetys.


Good luck.

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