If your heater won't turn on, first check that the thermostat is set to Heat, has power or fresh batteries and is set above room temperature. Then check the breakers for the furnace or air handler and the outdoor unit, the furnace power switch, the access panel and the filter. If there is still no heat, a failed control board, transformer, ignitor or safety switch is a common cause.
Quick checks before you call
- Thermostat set to Heat, set a few degrees above room temperature, screen working (replace batteries if blank)
- Breakers for the furnace or air handler and the outdoor unit are on. Electric heat strips may have their own breakers
- The power switch on or near the furnace or air handler is on
- The furnace or air handler access panel is closed tight. A safety switch keeps it off when the panel is loose
- The air filter isn't clogged
- No water in the drain pan under the air handler. A full pan or float switch can shut the system off
- On a gas furnace, the gas valve is on
Common causes of no heat
- Thermostat problemsDead batteries, the wrong mode, a schedule that was never changed from summer or a failed thermostat.
- Tripped breaker or blown control fuseA power surge or a short can trip a breaker or blow the small fuse on the furnace control board.
- Clogged condensate drainWhen the drain line backs up, a float switch cuts power to protect your home from water damage. This is common in Arizona because drains clog during the long cooling season.
- Failed transformer or control boardThese run the low-voltage controls. When they fail, nothing turns on even though the house has power.
- Ignitor, flame sensor or pressure switchOn gas furnaces, a failed ignitor, dirty flame sensor or pressure switch problem stops the burners from lighting.
- Blower motor failureThe system may hum or click, but no air moves through the vents.
- Outdoor heat pump not startingA failed capacitor or contactor can stop the outdoor unit. You may get some heat from backup heat strips, but your electric bill will climb.
Is no heat an emergency?
On a cold desert night it can be, especially for seniors, babies and anyone with health conditions. Never use an oven or grill to heat your home. If you use a space heater while you wait, keep it 3 feet from anything that can burn and plug it straight into the wall. If a carbon monoxide detector sounds, get everyone outside and call 911.
My AZ Pro repairs all brands of heat pumps, furnaces and heat strips in Surprise and Sun City West, and we never charge extra for nights, after-hours or weekends. More about our heating repair service.
Related prices
| Service | Typical Price Range |
|---|---|
| Service Call | $95 |
| Diagnostic Fee | $95 (waived with any repair) |
| Thermostat Replacement (Standard) | $150–$350 |
| Transformer Replacement | $200–$500 |
| Float Switch Replacement | $150–$350 |
| Drain Line Clearing | $100–$300 |
| Control Board Replacement | $400–$1,200 |
| Blower Motor Replacement (PSC) | $400–$900 |
Typical ranges for guidance only; your exact price is given in writing before any work begins. See our full price guide.