Diagnostic Guide

Why Your Furnace Is Not Heating

Furnace not heating? Learn the most common causes, repair costs, and when replacement is needed.

A furnace that will not heat can be caused by ignition problems, thermostat issues, or mechanical failures.

Common Causes

Thermostat Issues

Incorrect settings, dead batteries, or a faulty thermostat.

Dirty Air Filter

A clogged filter restricts airflow and can cause the furnace to overheat and shut down.

Ignition Problems

A faulty igniter, pilot light issues, or flame sensor problems prevent the burners from lighting.

Gas Supply Issues

A closed gas valve or gas supply interruption prevents the furnace from producing heat.

Blower Motor Failure

If the blower motor fails, heated air cannot circulate through the home.

Estimated Repair Costs

RepairCost Range
Thermostat replacement$75 – $300
Igniter replacement$150 – $400
Flame sensor cleaning/replacement$75 – $250
Blower motor replacement$300 – $800
Heat exchanger replacement$1,500 – $3,500

Should You Repair or Replace?

Most furnace repairs are affordable. However, a cracked heat exchanger on a furnace over 15 years old is a strong signal to replace the entire system.

See full HVAC replacement cost guide

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