I'm having problems with my home furnace "locking out". It will run fine, then for no known reason it will lock itself out. If I go down and reset the breaker, it will restart and continue to run until it locks out again (usually every four hours). Last year the board, igniter, sensors, condensate tubes and burners were replaced on the furnace. I live in rural area with limited HVAC contractors. I was with the contractor last time he serviced unit. Efficiency was running at 91 percent and everything checked out including the propane pressure. To eliminate the possibility, I also had the exterior regulator on the propane tank switched out. Any suggestions on cause?

Are you getting a flash code?