Before you call an HVAC technician and pay a $100–$300 service call fee, try these 10 fixes. Many furnace problems are simple enough to solve yourself in minutes.
10 Things to Check First
1. Check the thermostat: Is it set to HEAT, not COOL or FAN? Is the temperature set above room temperature? Replace batteries if the display is dim or blank.
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2. Check the circuit breaker: Find your electrical panel and look for a tripped breaker labeled "furnace" or "HVAC." A tripped breaker sits between ON and OFF. Flip it fully OFF then back ON.
3. Check the furnace power switch: There's a wall switch near the furnace that looks like a light switch. Make sure it's ON. It gets bumped off accidentally more often than you'd think.
4. Check the filter: A completely clogged filter can cause the furnace to overheat and shut down. Pull the filter out — if you can't see light through it, replace it before restarting.
5. Check the furnace door: Most furnaces have a safety switch that cuts power when the access panel is open or misaligned. Make sure both panels are fully seated.
6. Check the gas supply: Is the gas shutoff valve near the furnace open? The handle should be parallel (open) not perpendicular (closed) to the gas line. Also check that other gas appliances in your home are working.
7. Press the reset button: Most furnaces have a reset button (often red) on the burner assembly. Press it once. Don't press it more than once — if it trips again, there's a real problem.
8. Check the condensate drain: High-efficiency furnaces produce water. If the condensate drain line is clogged, the furnace shuts off. Look for a small white PVC pipe draining to a floor drain — clear any blockage.
9. Check for error codes: Look at the furnace's status light. Most modern furnaces blink error codes. Count the blinks and look up the code on the label inside the access panel.
10. Restart the furnace: Turn the thermostat down, flip the power switch off, wait 30 seconds, flip it back on, then turn the thermostat back up. This clears many electronic glitches.
When to Call a Tech
Call if: you smell gas (leave the house first), the reset button trips more than once, the furnace runs but produces no heat, or you see a yellow/orange flame instead of blue.
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