Promise Cabin 8 Furnace

Harold weekend host said thermostat wasn’t working. He changed the batteries and I gave an error code I think H6.

I tried to replace thermostat with one we had but I could not adjust the temp as the buttons would not work. I reinstated the old thermostat and it started working.

Next weekend guest said it was not working again. Checked vents, pressure switches and drains. One drain was plugged. Replaced. Still not working.

Manuel on top of furnace had a note the the burner breaker had tripped in 2017. I reset the breaker, added my note to the manual. The furnace is working. This is a picture of the burner breaker above the thermal coupler

Picture is of the breaker. It is a push button.