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Furnace not heating? What to check before you call
A furnace that won't heat on a cold Chicago night is stressful. These checks take a few minutes and sometimes solve it.
Check these first
- Thermostat: mode on Heat, set above room temperature, batteries fresh.
- Power: the breaker is on and the furnace switch, which looks like a light switch, is on. Make sure the blower door is closed fully, because most furnaces won't run with it open.
- Filter: a clogged filter can overheat the furnace and shut it down.
- Gas: confirm other gas appliances work.
- Vents: on a high-efficiency furnace, snow or ice can block the PVC intake or exhaust pipes outside.
- Condensate: a clogged condensate trap or drain can stop a high-efficiency furnace.
What the furnace is telling you
Most furnaces flash a code on the control board. Common faults include a failed igniter, a dirty flame sensor, a pressure switch problem from a blocked vent or drain, or an inducer motor that isn't running.
Stop and call if
- You smell gas. Leave the home and call 911 and your gas utility.
- A carbon monoxide alarm sounds. Get outside and call 911.
- The furnace shuts off again right after it restarts.
Never bypass a safety switch or reset a furnace over and over. Repeated lockouts mean something needs fixing.
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