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mranswer
mranswer, HVAC Mechanic
Category: HVAC
Satisfied Customers: 4809
Experience:  20 years experience running my own business
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Comfortmaker Furnace model GNJ075N12A1 burner wont stay lit.

Resolved Question:

Comfortmaker Furnace model GNJ075N12A1 burner won't stay lit. Checked all connections and just replaced the igniter and thermostat. Everything kicks on, even the burner once in awhile, but doesn't stay lit for long. Most times though, it doesn't kick on. Furnace was installed in 1995. I replaced the gas valve and flame sensor in 2004. The relay from the thermostat on outside of furnace if part 4000-01A19X82. The board is White Rodgers 50A55-438. The relay (inside furnace) is 4000-01E07AX191. I sure hope it's not another gas valve as I just cannot afford that right now. Thanks in advance for you immediate assistance.
Submitted: 1 year ago.
Category: HVAC
Expert:  mranswer replied 1 year ago.

I would first eliminate your wall thermostat as the issue only if the inducer will not even start up on the call for heat. Jump out the red and white wires that connect to it either at the t/stat or at the furnace end if the inducer does not run as explained. The furnace will start up. If it stays running then the t/stat is bad. If the flame goes out after starting then you have flame sensing issue, so that sensor could well be out again as a gas valve is typically going to open or not.

Customer: replied 1 year ago.

Where do I find the flame sensor and what does it look like? Not the igniter as I already replaced that.

Expert:  mranswer replied 1 year ago.

The flame sensor is part of the ignitor assembly -you said you replaced it in your post. Make sure it is clean and in the flame. Use some steel wool to lightly buff it.

Customer: replied 1 year ago.

Cleaned sensor. Turned furnace back on, flames lit and ran for several minutes. Flames shut off, but fans keep running and blowing the cold air continuously. If I flip the main switch on the side of the furnace off and back on, the system runs normal for several minutes. Again, the flame goes off and fans continue to run. The blower does not shut off for quite awhile, if at all.

Expert:  mranswer replied 1 year ago.

This may be a flame sensing issue or a problem within the mechanical part of the valve. The gas valve provides the flame sensing on this unit, so with the problem being the flame sensing then it looks like you need a new valve regardless of what is internally wrong here. The valve is probably pretty costly and there may be a retrofit kit made that you can install as this is getting old. You should have 24 volts being sent to that valve on the call for heat between terminals 1 and 3 on the 4 wire connector per the schematic that I see. This would prove that the board is fine.

Customer: replied 1 year ago.

Is there any way to take the valve off and test it?

Expert:  mranswer replied 1 year ago.
No, you can only make the voltage test as I described to eliminate anything external to the valve.
Customer: replied 1 year ago.

OK, we'll go from here. Thanks for your help.

Expert:  mranswer replied 1 year ago.
Thanks. Good luck here.
mranswer, HVAC Mechanic
Category: HVAC
Satisfied Customers: 4809
Experience: 20 years experience running my own business
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