Hello Everyone,

My Goodman GMT140-5D furnace will intermittently not ignite. What I mean is that the after the heat call from the t-stat, the inducer motor will come on, HSI igniter will glow for 15 seconds, but the burners will not ignite with flame. After 15 seconds and no flame, the igniter will shut off and try again, to the same result. This will continue until furnace locks out and will flash 1 continuous blink, which indicates an ignition failure fault code according to Goodman error code diagram.

This doesn't happen every time, but once every 1-2 days. It seems to mostly happen if the temperature inside the home was higher than the t-stat setting for most of the day (days are warmer in Colorado now, nights are still cold) and the furnace was not calling for heat for most of the day.

If I remove the rubber hose from the pressure switch, and blow in and out of the pressure switch, it will click, so I'm pretty sure it opens ok since I hear those clicks every time.

I've already replaced the igniter (twice), 120V/24V transformer, and the control board. I also had a an HVAC tech bend the HSI igniter bracket a little since he was sure that the igniter was too far from the gas burner and not sensing the HSI glow. That worked for a couple of days, but then the problem reappeared. I also already cleaned the flame sensor rod.

I'm thinking that the problem is either a bad gas valve or wiring (possibly from a bad grounding). I haven't replaced the gas valve yet. I'm thinking if I test the gas valve and it receives 24V when igniter glows, but doesn't open, then the problem is the gas valve. If I don't get 24V to the gas valve when the igniter glows, then the problem is the wiring/control board/ground, correct??

Can anyone tell me the proper way to check gas valve voltage? I'm thinking I should be checking continuity (ohms) by touching the gas valve terminals with the multimeter test leads (red test lead to red terminal, black lead to blue terminal) and the multimeter set the Ohms. If that's the proper way, anything higher than OL is good, correct? Or, is it better to check with multimeter set to AC voltage? Or should I remove the wires from the gas valve terminals and check with AC voltage? Again, I'm trying to see if the gas valve is actually receiving 24V from the control board...

Any other suggestions, ideas are greatly welcome...