Furnace Not Heating? 8 Common Problems and Fixes

The short version: when a furnace won't heat, the cause is usually the thermostat, a dirty filter, the pilot or igniter, or a failed part — and a few you can check yourself. For mechanical failures, a home warranty with heating coverage pays to repair or replace the part.

First, the quick checks

• Thermostat set to Heat and above room temperature, with fresh batteries?
• Air filter clean? A clogged filter can trip the furnace's safety limit.
• Breaker and the furnace's power switch on?
• Gas on, and the pilot light or igniter working?

8 common furnace problems

1. Dirty filter — chokes airflow and trips the limit switch.
2. Thermostat issue — wrong setting, dead batteries, or a fault.
3. Pilot light or igniter failure — no flame, no heat.
4. Dirty flame sensor — furnace lights, then shuts off.
5. Bad blower motor — heat but little airflow.
6. Failed limit switch or control board.
7. Cracked heat exchanger — a safety issue; shut it down and call a pro.
8. Clogged condensate line (high-efficiency furnaces) — trips a safety switch.

When a home warranty covers it

Mechanical failures from normal wear — igniter, flame sensor, blower, control board, limit switch — are what a home warranty is for. Heating is covered on even a Basic Plan on most warranties; you file a claim, a licensed technician is dispatched, you pay one service fee, and your plan covers the covered repair. See does a home warranty cover HVAC. Not covered: a problem that existed before coverage, or a furnace neglected into failure.

Key takeaways

• Check the thermostat, filter, power, and gas/igniter first.
• Igniter, flame sensor, blower, and control-board failures are covered by a home warranty with heating.
• A cracked heat exchanger is a safety issue — stop and call a pro.

Want your heat covered before winter? Get a free, no-obligation quote.

Frequently asked questions

Why is my furnace blowing cold air? Common causes are a thermostat set to on instead of auto, a pilot or igniter problem, or an overheating furnace shutting off the burner. Check the thermostat and filter first.

Does a home warranty cover furnace repair? Yes — heating is covered on most plans. Covered mechanical failures are repaired or replaced up to your plan's terms for one service fee.