Problem Center · Heating
Why Is My Furnace Not Heating?
The thermostat calls for heat, but the furnace doesn’t start, or starts and quits.
What could cause this?
- Ignition or flame sensor problems
- Pressure switch or venting problems
- Overheating and high-limit trips from restricted airflow
- Gas or oil supply issues
- Control board or thermostat wiring faults
What you can safely check
- Confirm the thermostat is set to Heat and above room temperature
- Check thermostat batteries if it has them
- Make sure the furnace service switch is on
- Check and replace a dirty filter
Don't open electrical panels or equipment cabinets, handle refrigerant, work on gas or combustion components, or bypass safety controls.
When it requires a professional
If you smell gas, leave the building and call your gas utility or 911 from outside. Otherwise, if the furnace still won’t run, or tries and shuts down repeatedly, request service — repeated resets can mask a safety problem.
How Air Mechanical diagnoses it
We follow the furnace’s sequence of operation to see where it stops, then find out why — ignition, flame sensing, venting, airflow or controls.
Every diagnosis starts with the system as it actually exists — equipment, controls, wiring and installation. The equipment has a brand. The problem has a solution.