When changing the temperature on my thermostat, the blower kicks on and only blows cold air. This drops the temperature about 2-4°.
After running for a few minutes, the blower shuts off. About 30 seconds later, it kicks back on and blows hot air.
I thought it was the old thermostat, so I replaced it with a Wyze thermostat. No change.
The furnace is a little older. It’s a Lennox Conservator G11E.
Any ideas would be lovely.
Based on a brief search I see your model of furnace is gas-fueled, has a two-stage ignition (a spark ignites a pilot, which in turn ignites the main gas), and has relatively primitive controls built into the gas valve assembly.
It sounds like what's happening is that the gas is not igniting reliably, or is not being sensed reliably, and so the control retries.
You can try watching the furnace to better understand where in its sequence things go awry. I'm not familiar with this specific model of integrated gas valve and ignition controller but I'd expect its operation to be as follows:
Somewhere in there the valve/control detects that the pilot flame ignited - probably between steps 3 and 4. This is called "flame proving." The electrode from which the spark jumps is likely also the sensor used for this.
If you observe the pilot and/or main gas igniting but then being shut off immediately that's an indicator that the flame proving is failing. You could try cleaning the electrode with fine sandpaper, emery cloth, or even a scouring pad like Scotch-brite.
Beyond that.. you might need to get a pro on site.
