My old thermostat turns on the burner and the fan both start normally.
When I install the nest the fan will start. The nest says heating but the burner won’t start.
The connections to the old thermostat are R,W,G,Y. With a jumper between Rc and Rh.
I made theses same connections to the nest and even added a C wire with no change.
if I remove the G and the Y wires there is no change.
The old thermostat works fine when reinstalled.
