Heater Not Working: What to Check Before You Call
Five checks outside the cabinet: thermostat, filter, the furnace switch, the breaker, and whether the outdoor heat pump is buried or iced solid. Then stop.
This is the short list. It is the same list we wish every no-heat call had already walked, because it separates a switch from a failed part. It is not a way to take the furnace apart.
Stop and leave if
You smell gas, or a carbon monoxide alarm is in its alarm pattern, or anyone feels sick the way a CO warning describes. Get out and call the gas utility or emergency services from outside. The rest of this page is for a cold house that is otherwise ordinary.
The checks
- Thermostat: Heat, fan on Auto, setpoint two degrees above the room. If a schedule keeps undoing you, set Hold. A blank screen is no power to the thermostat.
- Filter: if you cannot see through it, replace it with the same size, arrow toward the blower, system off while you do it.
- The switch on the side of the furnace that looks like a light switch: on.
- The breaker: on. Reset a tripped breaker once only. A second trip means leave it off.
- Heat pump outdoor unit: debris off the coil, fan not blocked. A little frost with a defrost cycle is normal. A solid block of ice that never clears is not, and you do not chip it with a shovel.
If the inducer runs and the burners never light, or the outdoor unit runs and the air stays cold, you are done with the list. Book heating repair or heat pump repair. Tell us which of these you already did. The longer version of no heat is why the heat is not working.
Common questions
I already changed the filter and it is still cold.
Then the filter was not the cause, or not the only cause. The next step is a diagnosis, not a second filter brand.
The heat pump is icy. Should I pour hot water on it?
No. You can crack the coil. A unit that does not clear itself in defrost needs service.
Is it worth calling if the breaker was off?
Turn it on once. If the heat returns and stays, you found it. If it trips again or never heats, call and leave the breaker off.
