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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 7709
Experience:  Furnace, A/C and heat pump specialist.
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I have an older furnace installed in the 1990's. M# GMP I

Customer Question

I have an older furnace installed in the 1990's. M# ***** I 100-4 with an intermittent pilot & (spark ignition).
When turned on the system would operate up to the spark but then no pilot lite.
I changed the circuit board and pressure switch.
Now the system runs thru burner ignition, but the gas valve keeps opening and closing very quickly as the system is running.
Any suggestions?
Max
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Have you tried cleaning the flame sensor?

Customer: replied 1 year ago.
thoroughly
Expert:  airheatman replied 1 year ago.

OK if flame sensor is clean, make sure the ceramic does not have a crack,Also unplug the wire and make sure connection is clean both on board and at sensor,Make sure there is no breakdown anywhere in that orange wire.. Do you have a meter that will read micro amp so we can see if we are getting at least 2.8 microamps to the board from flame sensor?

Customer: replied 1 year ago.
Ceramic looks good. I cleaned and checked all connections. I checked the sensor with a continuity tester and got a 'strong' continuity. I did not check it for micro-amps.
Expert:  airheatman replied 1 year ago.

Does your board have a light on it and if so does it give us an error code when burners go off such as 3 flashes then pause?

Customer: replied 1 year ago.
No diagnostic light non circuit board.
Expert:  airheatman replied 1 year ago.

OK.First make sure equipment has a good ground.Then check the micro amps and verify flame sensor is sensing flame and sending at least 2.7 micro amps to board to tell board to keep gas valve open.If so replace board.

Below is a short video showing how to check microamps:

https://www.youtube.com/watch?v=a5u044OJBc4