thermostat problem(s)

coburnbj

I have a gas furnace, and setting/controlling the thermostat has begun to drive me crazy. If I put the fan in the "on" position, it will run continuously (maybe it's supposed to do that, I don't know), and if I put the fan in the "auto" position, the fan will not come on until I change it to the "on" position. BUT, in the "auto" position, the cold air return begins to allow warm air to flow from it rather that sucking cold air into it. Thanks. coburn.eden@gmail.com

mts

well with auto fan , it kicks on to circulate heat away from the furnace to the rest of the house. when temp is met/predicted to be me or whatever the furnace turns off and hten the fan to keep cool air from being flushed through the system. obviously with the fan on it is constantly ulling air in and circulating. having hot air leak back is not really an issue if your heat is on.

that is just the way it works

Djeet

Setting the fan to "On" forces the blower to be turning, so you get air sucked into the return and blown out of the vents, regardless of if A/C or furnace is running. Are you getting hot air coming out when you turn it to "On"? If you get hot air blowing when you turn it to "On" and if setting it to "Auto" means the furnace burners fire up, but the blower never runs (you never get any air coming out of the vents), then a switch or relay is likely malfunctioning.

coburnbj

Thanks to mts and Djeet. I understand, from what you both say, that I don't really have a problem when the cold air return is leaking out warm air into the house when the fan is set on "auto." I've not seen that happen before and thought it might mean trouble.

grouch993

Normally for a furnace, the thermostat will indicate that the temperature has fallen below the set amount. The furnace will turn on and generate more heat. After a threshold, time or temperature, the fan will turn on and blow that warm air from the furnace through the vents. Once the thermostat goes over the set temperature, it will signal the furnace to turn off. The fan might stop at this point and still have warm air left in the ducts, or it will continue for some amount of time after the furnace has stopped heating and then turn off.

If the fan is not turning on or off when on automatic, or the furnace keeps turning on and off for short periods of time that might mean it is time to have the unit serviced.

Does that help at all?

mts

he probably doesn't hear the fan or is mistaking the fan for the furnace noise.

coburnbj wrote: »

Thanks to mts and Djeet. I understand, from what you both say, that I don't really have a problem when the cold air return is leaking out warm air into the house when the fan is set on "auto." I've not seen that happen before and thought it might mean trouble.

pretty much, with out a positive flow from the fan, the hot air is going to rise out of your ducts