How to Troubleshoot a Furnace That’s Not Heating

It’s one of the most frustrating winter problems: you wake to a freezing house and discover the furnace isn’t warming up. But before panic sets in, know that there are several common (and easy-to-fix) reasons for a non-heating furnace. This troubleshooting guide will help you diagnose and possibly fix the issue—even before calling a pro.

The most frequent cause of furnace issues is a thermostat set incorrectly or with dead batteries. Double-check settings, temperature, and the system’s power source. Even smart thermostats can get out of sync, so a quick review can prevent a chilly mishap. Has this ever happened to you?

A clogged filter starves the furnace of airflow, causing overheating and automatic shutdown. Swap in a new filter and see if the heat returns.

Furnaces rely on both power and sometimes gas supply. Reset any tripped breakers, check the power switch by the furnace itself, and—if applicable—confirm your gas valve is open.

Modern furnaces may flash error codes or LEDs. Check your user manual, decode the message, and follow basic fixes—sometimes saving hours on a service call!

This article continues with long-form sections about pilot lights, safety interlocks, exhaust vents, and when to bring in professional help to avoid bigger issues.

Troubleshooting your furnace saves time, discomfort, and often money. If these steps don’t bring the heat back, it may be time for a call to the pros—armed with the knowledge you’ve gained here.