Is it my furnace or my thermostat? Blows cold and can't shut it off
Furnace is a GrandAire combo with AC. Thermostat is a Hunter weekday/weekend programmable digital thermostat installed last year. FWIW, I rent this house.
Started 3 days ago. Furnace was blowing nothing but cold air and I couldn't shut it (the furnace fan) off at the thermostat. I reset the thermostat. I put it on A/C -- I did everything that I could thing of. The only way that I could stop the fan from blowing was to trip the breaker. Called landlord who called the HVAC folks. They came out and reset the roll-out switch (at least I think that's the correct switch). Ran properly for about 30 minutes. Called back, they came back out and said the switch was bad -- so they bypassed it and would replace the switch the next day. Which they did.
Went out about 1; came home and it was blowing cold air again. Called them back, they came back out (they're very responsive!) and took the cover off. The man said that they blew out the evaporator coil and that should take care of things.
Now, I'm not an HVAC genius (but my husband has more than a passing familiarity -- his dad is RSCS and used to do this for a living, but they're 400 miles away), but ????? Evaporator coil? For heat? From a Furnace?
It's a "self-igniter" (I'm not certain what the proper term is) -- it's my understanding that the thermostat triggers the flow of propane, which causes the igniter to light setting the whole process in motion. Maybe the thermostat triggers the igniter which causes gas to flow. The igniter is lighting properly, something is either shutting it down or stopping the flow of gas. The landlord says that something is cutting the gas off stopping the burners. He says it's around 5 years old -- but I'm not so sure about that.
I can't shake the "feeling" that the thermostat is somehow involved. Why couldn't I make the fan stop at the thermostat even when in the off position?
I'm just not enamored of confidence with these guys -- 4 trips in 2 days. Searching for a Second Opinion from the Collective Mind here!