Furnace running with thermostat off

furnaces always run for awhile after thermostat says heat off to cool down the heat exchanger.

how long did yours run?

Could be stuck relay on control board. If you have an older furnace, the fan could be controlled by a temp probe inside the duct. It looks basically like a dial that turns as the temp goes up or down. Another possibility is your T-stat is defective, Remove the wires from your T-stat and see if the fan goes off.

Will not stop running at all even with thermostat to off. I have to hit the breaker. It will run all night if I don't

is the fan switch on "on" instead of auto?

Furnace is a Lennox GH6D if that helps.

Is it the blower that runs, or are you generating heat and the blower is running. If the blower continues to run when the temperature of the blowing air is cool, then the sensor that shuts off the blower is defective. On older furnaces, as a previous poster said, there is a temperature sensor that has ordinary metallic contacts that sometimes stick. If you whack the side of the furnace and the blower stops, it is probably sticking contacts. Newer themostats have electronic controls that I don't know much about because I have an older fuirnace.

It is making heat. I have the thermostat to off and then flip back on the breaker and furnace is at full heat.

Heat and blower run

When mine did that a year ago, it was a bad thermostat. It thought it was cooler than what it read. They replaced it and it's been fine ever since. The whole unit was only 3 yrs old. Kathy

Hi, Relay stuck or newer ones have control board with relay on it. You did not mention furnace make and model.

Furnace is a Lennox GH6D if that helps.

Well it is now Monday so try contacting Lennox?

Lou

Since you've given no full model number and a very generic explaination it the same as saying this: I have a Buick. Sometimes in the morning it takes a while to start and then it keeps sputtering while its running. What could it be? Bubba

Maybe you've got a short in the wiring between the thermostat and the furnace. Mice that like to chew insulation will sometimes cause that.

Yeah, instead of disconnecting the thermostat at its location, it should be disconnected at the furnace for testing. Usually not so hard to find the wires. They are, at least in my case, either the only small wires that go to the furnace/AC or the there is just them and the small wires to the AC outside.

Sounds like sticky relay on the control board. I had a couple friends with this problem. They had replaced the thermostat four times (no kidding). I went there on unrelaed matter, and found the house unoccupied and about 80 degrees. I asked why was the heat up so high.....

Yes, I'm the fellow who actually repaired the problem.

Fuel line clog, or dirty air filter

Not finding a control board on this unit. It is prob. 20 or more years old. The thermostat runs down to a small transformer on the wall with

Still stumped

Probably an internal limit switch stuck. If so, this is a serious fire hazard.