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7 Reasons Your Car Heater Isn’t Working Properly

Kevin V

The roof, the roof, the roof is…freezing. You need to fix your heater.


A version of this story originally appeared on The Drive. is partnering with The Drive to share syndicated articles from experts who really know car maintenance.

As fall stretches into winter, most drivers aren’t too worried about their car’s heater. It worked last year, and the year before that, why wouldn’t it work this year? Well, fine drivers, life tends to throw curveballs at you, and guess what, your heater isn’t working properly anymore.

Heaters aren’t the mysterious beast most make them out to be. Heating systems consist of a heater core, a heater fan, the car’s coolant system, and your HVAC controls. As hot coolant is drawn into the heater core, the heater fan, controlled by the HVAC controls, blows that heat into the cabin as the cooled coolant returns back to the system. Though a simple system, a number of issues can arise causing your heating system to not function properly.

And now is the perfect time to learn what can go wrong and decipher your car’s heater is kaput. Follow along as The Drive’s whip-smart info team breaks down the top reasons why your car heater isn’t working properly and how to fix them.

car thermostats


7 Reasons Why Your Car Heater Isn’t Working Properly?

As with any faulty object, any of a host of reasons can prove to be the leading culprit. To better diagnose your car’s on-the-fritz heating system, let’s get into the reasons it can go bad.

Faulty Thermostat

A faulty or broken thermostat is the most common cause of your car’s failing heat. Stuck open or stuck closed, the part can not only cause issues with your heat but also your engine’s cooling system. One becomes an issue of comfort, the other becomes an issue of “Oh no, I’ve borked my engine.”

Low Antifreeze/Coolant

The second-most common issue is low antifreeze or coolant. When your coolant/antifreeze levels drop, the hot fluid can’t make it to the heater core, and thus, your cabin remains chilly. This can occur if the engine is working too hard and overheats or if it wasn’t properly filled.

car heating controls


Faulty Heater Fan

While you may be getting hot coolant/antifreeze into the heater core, the heater fan, the part that actually blows the heat into the cabin, can break or suffer an electrical short.

Faulty Blower Motor Resistor

If the blower motor resistor is broken, you might have issues setting the fan speed or getting air at all.

Clogged Heater Core

Occurring less often than the above issues, debris and particulates that make it into the coolant system can clog your heater core. This can happen when a radiator rusts from the inside or if debris gets through the radiator and lodges itself into the heater core. Either way, you’re looking at refurbishing your heater core or straight-up replacing it.

Leaky Radiator

A leaky radiator could prevent coolant from reaching your heater core and could damage your engine, at worst.

Faulty HVAC Controls

Simply put, your car’s buttons, knobs, or haptic feedback touchscreens may not be triggering the heating system. Shorts, broken dials, and bad touchscreens can all lead to malfunctions that prevent your heater from working.

Faulty Wiring or Blown Fuses

Similar to your broken HVAC controls, your car’s wiring could be broken or have a short in it. This would mean the heater isn’t triggered when the driver commands it to function. Not good.

car heater vents


Here’s How To Fix a Broken Thermostat

To assuage your fix-it fears and show you just how easy DIY repairs can be, The Drive put together an easy-to-follow guide on how to fix a broken thermostat. You will need to purchase new coolant and a new thermostat.


Working on your car can be dangerous and messy, so here’s exactly what you’ll need to ensure you don’t die, get maimed, or lose a finger and that you keep your jeans, shirt, and skin spotless—hopefully.

  • Mechanic’s gloves
  • Safety glasses

Everything You’ll Need To Fix a Broken Thermostat

We’re not psychic, nor are we snooping through your toolbox or garage, so here’s exactly what you’ll need to get the job done.


  • Drain bucket
  • Selection of wrenches


  • Coolant
  • New thermostat (before you buy, make sure it fits your vehicle)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

How To Fix a Broken Thermostat

  1. Let the car cool for 15 to 20 minutes.
  2. Locate the thermostat. It will be at the base of the radiator, in between the core and the main hose.
  3. Remove the radiator cap.
  4. For better clearance, lift up the front end of the vehicle.
  5. Place a bucket underneath the radiator and drain the coolant by detaching the hose.
  6. Remove and replace the thermostat.
  7. Reattach the hose to the radiator.
  8. Add the coolant and place the cap back on the reservoir.
  9. Lower your car.
  10. Start the engine.
  11. Wait to see if the heat comes on.
  12. Take a test drive.
  13. Check to make sure the coolant level hasn’t dropped.
  14. If it has, refill it as necessary.

You’re done!

how to fill antifreeze


How To Fix Low Antifreeze

The second-most common culprit is that your car has low antifreeze or coolant. Thankfully, it’s far less time-consuming than replacing your thermostat. All you’ll need is a funnel and new coolant. Ready?

  1. After letting the car cool, remove the radiator cap and place the funnel in the opening.
  2. Pour in the new coolant until the reservoir is full. You may need to grab the main coolant hose and physically pump the coolant to ensure there are no air pockets.
  3. Replace the radiator cap.
  4. Start the car, and check if the heat comes on.

That’s it!