A furnace that won’t ignite is usually blocked by a simple fault: a thermostat setting, a dirty filter, a closed gas valve, a dirty flame sensor or a failed igniter. Check the first three yourself. Leave the sensor, igniter and gas work to a licensed pro.
Climate Pros Tucson matches homeowners with licensed local pros who handle furnace repair.
Why does a Tucson furnace fail on the first cold morning?
A Tucson furnace can sit unused from spring through fall. Dust, spider webs and insect nests settle in the burner area and on the flame sensor over a long summer. The furnace then gets asked to run on the first cold night, when it is most needed. Winters are mild here, with fewer than 12 nights a year at or below freezing at the airport, so a furnace may go months between runs.
If your home runs on a heat pump, there is no furnace to light. See what is a heat pump.
What can you check safely?
- Set the thermostat to heat and a temperature well above the room reading. Replace its batteries if it has them.
- Check the air filter. A clogged filter can trip a safety switch.
- Make sure the furnace switch (it looks like a light switch near the unit) is on and the breaker has not tripped.
- Confirm the gas valve handle is parallel to the pipe, meaning open.
If you smell gas, leave the house, then call the gas utility or 911 from outside. Do not flip switches. Southwest Gas is the natural gas utility in the area.
What are the common causes inside the furnace?
- Dirty flame sensor. The burner lights and shuts off after a few seconds because the sensor can’t confirm the flame.
- Failed hot surface igniter. A cracked or worn igniter glows weakly or not at all, and the burners never light.
- Pressure switch or inducer problem. The draft motor has to prove airflow before gas flows. A stuck switch or a clogged vent blocks the start.
- Bad control board or thermostat wiring. The furnace gets no signal to start.
- Heat exchanger or safety lockout. A furnace that locks itself out after several tries needs a pro.
Should you keep trying to restart it?
No. Many furnaces lock themselves out after several failed tries, and repeated resets can hide the fault pattern the pro needs. Try once or twice after the basic checks, then stop. See furnace blowing cold air if it runs but doesn’t heat.
Is carbon monoxide a concern?
A malfunctioning gas appliance can produce carbon monoxide. If a detector goes off, or anyone feels dizzy or nauseous, leave and call 911. Read carbon monoxide in a home for more.
When should you call a pro?
Call when the furnace locks out, the burner lights and shuts off, you hear clicking with no flame, or the system is old and failing more often. Check that a pro holds a current Arizona Registrar of Contractors license at roc.az.gov. See signs your furnace is going out and furnace repair. The Tucson HVAC hub lists areas covered.
Getting a furnace that won’t light fixed
For a furnace that won’t light, we match you with a licensed pro who diagnoses it and tells you what it needs before the work begins. Call (520) 353-2520 and we’ll match you with a licensed local pro.