Lennox G50UH(X) Inducer Motor Problem

While visiting my Mom for the holidays, we've been having trouble with her furnace and I haven't come across any good information about this problem or how to fix it.

When the thermostat calls for heat, the inducer/combustion motor cycles off and on several times before the ignitor kicks in. Once I have a flame, there are no other problems. It's pretty annoying hearing the relays clicking so much, but that seems to be the only problem.

Before this, I have already cleaned the flame sensor which was looking a little grimy. I've also checked for any error codes and came up empty. The LEDs show that everything is operating normally.

Any ideas?

 

I'd check the stat.

Does the furnace start normally if you remove the stat and jump R (24VAC) to W (heat terminal)?

 

When the thermostat calls for heat, it does so by taking voltage from the R terminal on the furnace and applying that voltage to the W terminal on the furnace.

Any time you have 24 VAC being applied to the W terminal the inducer motor should turn on and stay on.

So the proper way to check what is happening is to use a multimeter to see if the inducer motor is staying on when there is 24 VAC to the W terminal.

If you do, that suggests that the thermostat isn't switch on voltage to the W terminal reliably, or perhaps the voltage to the R terminal is being interrupted.

If the voltage to the W terminal is on and the inducer motor isn't starting and staying on reliably, you have a bad circuit board that needs to be replaced.