Why is my furnace not turning on?

What usually stops a furnace from starting

Modern furnaces run through a strict safety sequence before they ever light: thermostat call, inducer fan, pressure switch, ignition, flame proof, then blower. A failure at any step shuts the whole process down. The most common culprits are simple, including a thermostat with dead batteries, a breaker that tripped, or the furnace's own light-switch-style power switch getting bumped off. Beyond those, a severely clogged filter can overheat the furnace and trip the high-limit safety, a dirty flame sensor can shut the burners off seconds after ignition, and hot surface ignitors simply wear out over time. On high-efficiency models, a blocked condensate drain will also lock the furnace out.

Things a homeowner can rule out first

• ✓Set the thermostat to heat and raise the setpoint several degrees above room temperature
• ✓Replace the thermostat batteries if it has them
• ✓Check the breaker panel and the power switch mounted on or near the furnace
• ✓Swap in a clean air filter
• ✓Confirm other gas appliances in the home are working, which rules out a supply interruption

Where the do-it-yourself work should stop

If the furnace still will not fire, leave the burner compartment, gas valve, and safety switches alone. Bypassing a safety control or repeatedly resetting a locked-out furnace can be dangerous. A heating technician can read the control board's diagnostic codes, test the ignitor and sensors, and find the actual failed component. With 32+ years of experience and a Master HVAC Technician owner, PJ MAC HVAC works on gas and oil furnaces, boilers, and heat pumps of every major brand.

A house with no heat cannot wait until morning, so PJ MAC HVAC takes heating calls around the clock, every day of the year.