Furnace Not Heating? 8 Reasons Why (and What to Do)

1. Thermostat Set Incorrectly

It sounds obvious, but always check first. Ensure it's set to HEAT, the temperature is above the current room temperature, and the fan is on AUTO (not ON, which blows air even when not heated).

2. Dirty Air Filter

A severely clogged filter restricts airflow so badly that the furnace overheats and triggers a safety shutoff. Replace the filter and reset the furnace by switching it off for 30 seconds.

3. Tripped Circuit Breaker

Check your breaker panel. A tripped furnace breaker will cut all power. Reset it once — if it trips again immediately, call a professional. A recurring trip indicates an electrical fault.

4. Pilot Light or Igniter Failure

Modern furnaces use electronic igniters. If you hear clicking sounds but the burners don't light, the igniter may be cracked or failed. This is a common, relatively inexpensive repair.

5. Flame Sensor Dirty

A dirty flame sensor causes the furnace to light briefly then shut off within seconds. The sensor needs cleaning — a task for a qualified technician as it involves working near the burner assembly.

6. Blocked Vents or Registers

Walk through your home and ensure all supply and return registers are open and unobstructed. Closed vents create pressure imbalances that cause furnace safety shutdowns.

7. Inducer Draft Motor Failure

If you hear your furnace attempt to start but never fully ignite, the inducer draft motor may have failed. This motor vents combustion gases before ignition — if it can't run, the furnace won't start.

8. Cracked Heat Exchanger

This is the most serious issue — a cracked heat exchanger leaks carbon monoxide into your living space. Signs include yellow/orange flame (should be blue), soot marks near the furnace, and CO detector alerts. If you suspect this, shut the furnace off and call us immediately.