How to Troubleshoot a Car Heater

by Ross Glyn

Getting in your car on a freezing morning, turning on the heater, and receiving a blast of cold air is no fun. The heating system works by diverting coolant into a heater core. An electric fan blows air through the heater core, which is then blown through ducts into the vehicle compartment. The car heater is a relatively simple system and there are a number of troubleshooting steps you can take before taking your car for a costly visit to a mechanic.

Troubleshooting Steps

Check beneath the hood to see if there is sufficient coolant (antifreeze) in your vehicle.

Start the car engine and allow it to warm up. Turn the heater on and listen for the blower. If the blower is not running, the problem could be related to a blown fuse.

Locate the fuse box beneath the steering wheel. Consult the fuse diagram on the box to see where the fuse for the heater is located. Pull the fuse out and check that that it is not broken or burned out.

Look under the hood and find the hoses that connect to the heater core. The hoses usually connect to the heater at the firewall and are either black or red. If the hoses are not hot to the touch, the coolant may not be circulating properly. It may be time to replace the heater core. A mechanic should do this.

Place your hand on the floor of the passenger side. If it is wet, or has a sweet odor, then the heater core may be leaking and you will need to replace it.


  • check A defective heater control valve or thermostat can also be the cause of restricted coolant flow through the heater core.
  • check If the problem is fuse related, make sure to replace it with one of the same amperage.
  • check Check both the inlet and outlet heater hoses for heat.
  • check The hoses connecting to the heater core are usually about the thickness of a garden hose.
  • check A rear-engine configuration or front-wheel drive vehicle are usually more difficult to troubleshoot. You may need to consult a mechanic.
  • check The blower, or electric fan may be defective.
  • check If the blower is running, it could be that the hot air is being misdirected. The heating system has small gates that open and close to direct the air. These gates could be malfunctioning.
  • check .


  • close When checking the hoses for heat, it is best not to touch the hose directly. Rather, place your hand directly above the hose.

About the Author

Ross Glyn began writing for film and television in 1986. He wrote and directed the film “After The Rain” as well as the play “Soweto's Burning.” He is a member of the Writers Guild Of America, the Screen Actors Guild and the American Federation of Television and Radio Artists. Ross holds a performer's degree from the London Academy of Music and Dramatic Art.

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Photo Credits

  • photo_camera car heater vent image by robert mobley from