Furnace doesn't shut off?

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?

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.

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!