Why Won’t My Furnace Stay On or Heat the House?

Few things are more frustrating than turning on your furnace on a cold day only to find that it won’t stay on or isn’t heating your home properly. When your furnace starts cycling on and off or blowing cold air, it’s often a sign that something’s not working as it should.

If you’re wondering, “Why won’t my furnace stay on or heat the house?”, there are several possible causes, some simple to fix, others requiring professional attention.

Common Reasons a Furnace Won’t Stay On

A furnace that doesn’t stay on long enough to heat your home may be dealing with one of these common problems.

1. Dirty or Clogged Air Filter

A dirty air filter is one of the most frequent culprits. When the filter is clogged, airflow becomes restricted, causing the furnace to overheat. To protect itself, the system shuts down prematurely. Replacing or cleaning the air filter can often solve this issue quickly.

2. Malfunctioning Thermostat

If your thermostat isn’t working properly, it might not be communicating correctly with your furnace. This can cause the furnace to turn off too early or fail to reach the desired temperature. Make sure your thermostat has fresh batteries and is set to the correct mode before calling for service.

3. Flame Sensor Issues

The flame sensor ensures the gas burners are lit properly. If the sensor is dirty or faulty, it may shut off the gas supply as a safety measure, causing your furnace to stop heating. Cleaning or replacing the flame sensor often fixes this issue.

4. Blocked or Restricted Air Vents

Blocked vents can cause uneven heating and make your furnace work harder than necessary. Check that all vents are open and unobstructed by furniture or rugs to improve airflow.

5. Faulty Limit Switch

The limit switch is a safety device that turns the furnace off when it overheats. If it malfunctions, it might shut down the system even when temperatures are normal. This issue typically requires professional repair.

6. Pilot Light or Ignition Problems

Older furnaces have pilot lights that can go out, while newer models use electronic ignition systems. If your furnace isn’t producing a consistent flame, it won’t heat properly. Relighting a pilot or replacing a faulty igniter may be necessary.

7. Dirty Blower Motor

The blower motor distributes heated air through your ductwork. If it’s clogged with dust or not working correctly, the system can overheat and shut down. Regular cleaning and maintenance help prevent this.

Why Your Furnace May Run but Not Heat

If your furnace turns on but blows cold air or fails to warm your house, it might be caused by:

• Low gas supply or closed gas valve

• Faulty burners or clogged components

• Malfunctioning thermostat sensor

• Electrical issues affecting the control board

  
  

Because these involve electrical and gas components, it’s safest to call a professional to inspect and repair the system.

The Importance of Regular Furnace Maintenance

Most furnace problems start small but grow over time if left unchecked. Scheduling routine maintenance helps prevent issues like short cycling, airflow restrictions, or ignition failures. During a maintenance visit, technicians will clean internal components, check safety features, and ensure your furnace is operating safely and efficiently.

At Van Bremen’s Heat & Air, our technicians specialize in diagnosing and repairing furnace problems quickly and effectively. We also offer professional maintenance services to keep your system running smoothly all winter long.