Thread: furnace fan

furnace fan will not shut off. could it be the thermastat?

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Go to the home thermostat. It should have a switch that turns the furnace fan on and off...regardless if the furnace is running or not the fan will be on, if the switch is in the on/ run position....
Place it in the off position. It will still come on when the furnace comes on. On older homes this switch may be located at the furnace with a pull push style of switch. Maybe ur kids were playing with it...

Good luck

Fan switches do fail in the closed/ on position on occasion. Rule out the T- stat/ summer on switch, but don't discount a failing/ failed switch.

One way to check-- smack the switch with something like a pair of channel locks or some other tool. Often times, the switch will shut off/open when hit, but stick when run again.

Hi limit switch may be defective.

Originally Posted by Stephen G

Go to the home thermostat. It should have a switch that turns the furnace fan on and off...regardless if the furnace is running or not the fan will be on, if the switch is in the on/ run position....
Place it in the off position. It will still come on when the furnace comes on. On older homes this switch may be located at the furnace with a pull push style of switch. Maybe ur kids were playing with it...

Good luck

What I usually see on a thermostat is two fan switch positions on the thermostat. "Auto" and "Off". Move the switch to the "Auto" position. If the fan continues, while the burner is off, then it's time to call a HVAC tech.

An HVAC tech will know exactly how hard to hit the switch with his channel lock pliers.

An HVAC tech will know exactly how hard to hit the switch with his channel lock pliers.

Hit it hard enough, and I guarantee the switch will open...

Or the panel breaker will trip...it's a practised move....

Originally Posted by william k fowler

furnace fan will not shut off. could it be the thermastat?

How old is the house? Is it Energy Star rated?

Newer homes built with Energy Star specs have a ventilation controller mounted near the air handler that overrides the t-stat fan switch.

The fan is turned on as determined by a preset program as a way to bring in outside air from a vent mounted on an exterior wall that is ducted to the return air duct.

Some t-stats have a program that runs the fan for basic filtering during preset times of the day also.

Most likely the fan/limit control located on the furnace needs adjusting or replacement.

Most common are Honeywell units which have a element extended into the heat exchanger. As the temperature rises in the heat exchanger, the control rotates a disc which in turn closes a micro switch to turn the fan on. If the temperature continues to rise, the disc rotates further and opens the burner circuit to prevent overheating. It may simply be that the "fan off" setting is just too low. Moving it to a slightly higher position may solve the problem. Otherwise the control should be replaced. Many very old systems have the fan/limit control installed in the plenum above the heat exchanger.

I find it strange there are so many posted scenarios when William did not say what furnace fan he was talking about.

Originally Posted by Eric Barker

I find it strange there are so many posted scenarios when William did not say what furnace fan he was talking about.

Hmmmmm.........well, I certainly "assumed" he was referring to the blower fan, but the induction fan would be a very different problem............

But even stranger, William hasn't responded to all this great commentary with what he did or what the problem actually was.

I guess people forget their manners too. Asks a question, doesn't even say thank you in in original post.