Tempstar Furnace Intermittent Startup
We have a natural gas-fired Tempstar furnace that sometimes will not start-up. It is controlled by a setback thermostat. In the morning it normally fires up fine for the first heating cycle, but usually gets "stuck" on the second cycle. By stuck, I mean we get a yellow flame (coil heating up?) for a few seconds, then a blue flame (burner jets?) for a few seconds, then a click and the blue flames go out. The cycle is repeated a few times. Sometimes the burners successfully light and other times not. If the burners do not light within about five tries, a red light on a module inside the furnace comes on - which I'm guessing is an error light of some kind.
If I turn the system off (toggle switch on side of the furnace) and back on, it sometimes will get the system running again. Sometimes not...
We've had service technicians out twice. The first said everything looked fine, did a cleaning and things seemed to work okay until the end of the season when the same issue started occurring. This year the system ran for a few weeks without issues, but now it seems to be occurring again. A technician was out to investigate last week and said he found a loose wire, which he reinstalled. However, the next morning we had the same issue... it fired up for the first cycle and failed to fire up on the second. I turned the system off and it ran.
Any chance this is related to the thermostat itself? I think not, but I'm not a technician.
Any good advice on where to go with this would be appreciated. I hate to keep paying $100 per trip for technicians who don't seem to be able to find and resolve the core problem.