So last night it started getting cooler in my house, not intolerable but it was 5-7 degrees cooler than I like so I looked at the old digital thermostat and it read 65 degrees. Since it is set to 72 this made me wonder "why isn't the furnace kicking on?" Slide the various setting levers on the thermostat back and forth and the fan comes on but no heat (gas furnace BTW).
Scamper downstairs to the mechanical room and turn off the main switch on the furnace itself (a standard light switch), wait a moment and turn it back on, taa daa, off to the races and the furnace comes on just as it should and runs as it should. Happy times!
Fast forward to 5 am and it's chilly again. No heat coming on. Again.
What do we think, tired old thermostat not recognizing the need to turn on and just due for replacement? Something else?
I imagine this is a totally different issue since mine is all electric, but several years ago it started randomly tripping the main service breaker in the attic. you could reset the breaker and it would run fine. The trips became more frequent until it melted the big ass 220v breaker into smoldering plastic. There wasn't any problem with the system, the breaker just went bad. Which was no less terrifying at 2 am.
Could you check some kind of trigger output voltage on the thermostat? I have almost no idea how these things work...
HVAC tech at work has suggested a dirty flame sensor. Will be cleaning it this evening.
I had something similar years ago, also in a damn cold winter. IT was the temp sensing safety thermocouple. It would fire up, but the thermocouple wasn't reading heat so it shut down again. $5 part but man it took some serious disassembly to replace it, like a couple of hours to tear down to reach it but 90 seconds to change it. Then reassembly was the reverse etc.
Adrian_Thompson said:
I had something similar years ago, also in a damn cold winter. IT was the temp sensing safety thermocouple. It would fire up, but the thermocouple wasn't reading heat so it shut down again. $5 part but man it took some serious disassembly to replace it, like a couple of hours to tear down to reach it but 90 seconds to change it. Then reassembly was the reverse etc.
Same situation happened to me once. Since I didn't have a replacement thermocouple on hand, pulled it out, scrubbed it with steel wool or scotchbrite and put it back together. Fired right up, and has continued working since.
Was easy access in my furnace though-- no serious disassembly.
Was used to having to do the equivalent with a positive ventilation hot water heater, but that needed it so frequently I eventually just said berkeley it and replaced it with an electric.
