G23Q2-50-4, furnace starts, vent blower starts, ignites pilot, ignites burners but sometimes the main blower fails to run. Furnace then runs for several minutes before shutting down, then starts up again in several minutes and goes through the same process.

Presumably the furnace shuts itself down due to overheating (since the temperature called for by the thermostat is never reached) and once the overheating sensor resets, the furnace starts up again to try and satisfy the thermostat.

This is an intermittent thing, sometimes the main fan works and all is ok. I removed the electronic thermostat and replaced it with the original honeywell round style one and have the same results, intermittent main fan.

Also of note, when the furnace is not running, I've turned the main fan switch on the thermostat from "auto" to "on", sometimes this turns the main fan on, and sometimes it doesn't. (so intermittent here as well.)

Thanks for any help you can offer