Why Isn’t My Heater Working? 5 Common Reasons Your Furnace May Be Broken

It is normal for homeowners to notice that their furnace is no longer keeping them warm. A furnace that isn’t blowing hot air can be frustrating, but don’t panic. There are several issues that commonly cause this problem, and many can be fixed without calling a professional. Identifying the cause will help you determine if a DIY repair is possible or if it’s time to contact an HVAC company.

Heater Working

1. Thermostat Issues

One of the simplest things to check is the thermostat. Confirm it is set to “heat” and the desired temperature is higher than the current room temperature. Also check that any switches controlling individual zones are set properly. Thermostats can malfunction, so replace it if adjusting settings does not solve the problem. Make sure the furnace is receiving the “call for heat” signal from the thermostat.

2. Dirty or Clogged Air Filter

A dirty air filter blocks airflow and makes the furnace work harder. This symptom could indicate it’s time to replace the filter. Filters should be changed every 1-3 months depending on your system and household. A clogged filter can also cause the heat exchanger to accumulate debris and fail prematurely.

3. Pilot Light Out or Gas Valve Problem

If the furnace uses gas, check that the pilot light is lit. The pilot light provides continuous flame needed for the main burners to ignite when heating is demanded. Have the gas company relight it if out. A faulty gas valve can also prevent gas from flowing to the burners. This is not a DIY fix and requires a professional.

4. Blown Fuse or Tripped Circuit Breaker

Furnaces require electricity to operate various components like the blower motor and control board. Check the fuse box for tripped circuit breakers or replace any blown fuses related to furnace operation. A surge when the furnace first tries to ignite could cause this.

5. Heat Exchanger Cracks or Leaks

Over time, the heat exchanger that warms air can develop small cracks or leaks, allowing combustion gases to mix with the airflow instead of being vented outside. This is dangerous and must be repaired by a professional. Heater not blowing hot air and other issues could indicate an exchanger problem requiring replacement.


While some furnace problems have simple DIY solutions, any issues involving gas, electricity or structural components require an HVAC technician. 

Signs that point to needing professional help include suspicious smells, loud noises, flames appearing abnormal, or the problem persisting after checking basic issues. Don’t take safety risks with gas or electrical systems. An annual furnace inspection and tune-up can also prevent bigger problems and keep your system running efficiently.For more tips on troubleshooting common issues that could be preventing your heater from producing warm air, you can check out the article titled “Heater Not Blowing Hot Air?’’