A cold house on a winter morning usually means a furnace that has stopped for a reason. Before you call for heating repair, run through this five-minute checklist. It solves a surprising number of no-heat calls.
Five things to check
- Thermostat. Set to heat, set above room temperature, batteries fresh.
- Breaker. Find the furnace breaker in the panel and make sure it is on. If it trips again, stop and call.
- Furnace switch. There is a light-switch style disconnect on or near the furnace. It is easy to bump off.
- Filter. A clogged filter overheats the furnace and trips the limit switch. Replace it.
- Blower door. The door must be fully closed to press the safety switch.
What the technician will look for
If the furnace still will not run, the fault is usually in the ignition or safety chain. A dirty flame sensor lets the burners light and then cuts them off within seconds. A cracked igniter clicks but never glows. A pressure switch that cannot prove the inducer is running keeps the gas valve closed. A limit switch trips when airflow is restricted. All of these are standard furnace repairs that a stocked truck fixes on the first visit.
Cold air from the vents
If the blower runs but the air is cold, the burners are not staying lit. That points again to the flame sensor, igniter or gas supply. On a heat pump, cold air in heating mode can mean a reversing valve or defrost problem. See heat pump repair.
When it is an emergency
If you smell gas or a carbon monoxide detector sounds, leave the house and call the gas company or 911 first. For any other no-heat situation, 24 hour heating repair is a call away at (855) 459-5498. Find the no-heat repair page for your city.