Furnace doesn't shut off?

[Nate R]

Tenant called and said that her furnace will come on, but does not shut off on it's own.

She woke up and the house was ~90 degrees! Sounds like it's running like this repeatedly. It will come on until she shuts it off.

Nat Gas, forced air.

I'm assuming the likely cause is the thermostat going bad?

 

[Bob NH]

Could be lots of things. Where is the emergency switch? Sounds like your tenant needs a little training on how to turn things off.

I would suspect thermostat, or thermostat wire, or the furnace control equipment.

Someone with a multimeter could check it in about 5 minutes.

Or you could call a service man to come check it out for $125 to $200 minimum charge.

I would immediately call the tenant to turn off the furnace at the emergency switch; then check out the thermostat.

 

[Sponsor]

 

[GrumpyPlumber]

If she's turning it off with the thermostat then it's probably the thermostat, easy fix.
If she has to shut the furnace off, it's probably a relay, you'll need a tech for that.

 

[Nate R]

It was the thermostat. Digital thermostat. She was shutting it off by flipping the switch on the stat to off.

Replaced it with a new one and it works fine.

Thanks!