🔥 Furnace Troubleshooting Guide
Click on a problem below to expand the troubleshooting steps.
🚨 Furnace Won’t Start (Click to Expand)
- Check if the **thermostat** is set to "HEAT" mode and the temperature is set above room temperature.
- Ensure the **furnace switch** and circuit breaker are ON.
- Check if the **blower compartment door is securely closed**.
- Inspect the **LED diagnostic code** on the control board.
- If the LED flashes an error code, refer to the LED code chart.
💨 Blower Runs Continuously (Click to Expand)
- Check if the **thermostat fan setting** is set to "AUTO" instead of "ON".
- Look for an **open limit switch or stuck relay** in the control board.
- Inspect the **blower motor capacitor** (test it with a multimeter).
- If the capacitor is faulty, **replace it**.
- If the blower still runs non-stop, the **control board may need replacement**.
⏳ Furnace Turns On & Off Quickly (Short Cycling)
- Check the **air filter** – a clogged filter can cause overheating.
- Ensure the **flame sensor is clean** and positioned correctly.
- Verify the **pressure switch and exhaust vent** for blockages.
- Inspect the **inducer motor** – if it’s not running, it may need replacement.
- Check the **heat exchanger** for cracks (a serious safety issue).
🔥 Ignition Failure (Click to Expand)
- Check if the **igniter glows** during startup.
- If the igniter does NOT glow:
- Test the igniter with a multimeter (should have **40-90 ohms resistance**).
- If the igniter is bad, **replace it**.
- If the igniter glows but no flame appears:
- Check the **flame sensor** – clean it with a scotch pad.
- Test the **gas valve** – ensure it clicks and opens.
- If the gas valve does not open, the **gas valve or control board** may be faulty.
💨 Ventilation / Pressure Switch Issues
- Check for **blocked exhaust vents** (snow, debris, or bird nests).
- Inspect the **pressure switch hose** – make sure it's not clogged or cracked.
- Use a multimeter to **test the pressure switch** – if it fails, replace it.
- Check the **inducer motor** – if it doesn’t start, it may need replacement.