I have a lennox G24M3/4-100A-2 forced air gas furnace. Recently it has started to not light and then go into watchguard mode. After resetting, and then calling for heat, the draft inducer kicks on and a few seconds later I hear the electric spark of the ignitor clicking but the burners won't fire up. I thought maybe the gas valve wasn't turning on, so to check if there was gas, I manually lit the burners with a lighter and the burners would fire up like they should. The furnace would then run normally until it reaches the set temperature on the thermostat and then turns off like it should. When it calls for heat again it repeats the cycle of going into watchguard mode. I can keep the furnace running if I light the burners manually with a lighter each time it calls for heat after resetting the watchguard mode.

I cant directly see the spark on the ignitor because the burner is in the way but I see the light of the spark going off and on when its making the clicking sound. Its almost like the ignitor is producing too weak of a spark to ignite the gas. Thinking the ignitor was bad I ordered and installed a new ignitor but it didnt resolve the issue. Any ideas on what is causing this problem?

 

Welcome to the forums.

It sounds like the HSI (hot surface igniter) may need to be replaced or moved closer to the burner.


G24m manual - pdf