Work Performed: Returned for a recurring no-heat call on a furnace with ongoing nuisance flame rollout switch tripping. After extensive testing, I found that when the gas valve was turned off, the furnace would occasionally backfire, and at times the gas valve did not close fully. This caused the burner flames to continue “candling” inside the cabinet, heating up the rollout switch and causing it to trip. Diagnosis: The gas valve is failing internally and is not sealing properly. This is causing delayed shutdown, candling flames, and intermittent backfire — all of which can trigger flame rollout safety devices. Recommendation: The gas valve must be replaced and properly set up and adjusted after installation to ensure safe and stable furnace operation.