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Why Your Car Heater Is Not Working (And Easy Solutions)

Man`s hand on car heater or conditioner, regulates temperature in automobile while drives. Car`s accessories or panel. Conditioning concept.

Nothing feels worse than cold air blowing from your car’s vents in the dead of winter. When your car’s heater stops working, your daily commute feels more like torture. The good news? We know why your car’s heater might not be working, and we have some quick and easy solutions to help you.

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Quick Explanation: How Your Car HVAC Works

In a perfect world where your car’s heater is working, here’s what the process looks like:

If your recirculation button is turned off, the air is taken in from outside. It goes through a cabin air filter and gets churned through your blower motor. The air passes through an A/C evaporator.

There’s a door that toggles the air’s direction from there. If your car is set to cold air, it will go right to your vent. If it’s set to “heat,” the door will direct the air through a heater core which gives a lot of warm energy to the air.

The final leg of the journey is the warm or cool air going through your vents. Three independent doors control the three modes for your HVAC: air to your face, legs, or defrosters.

Why Your Car Heater Is Not Working

If you’re feeling lukewarm or cold air when your dial is set to hot, then something is clearly wrong. Something isn’t working the way it should.

In this section, we’ll explain some of the common causes and give you easy solutions to fix them (as easily as possible).

Not Enough Coolant

The one bit of science that we didn’t talk about is the role of coolant. This is the secret sauce when you want to transform the temperature of the air in any given situation.

Coolant is really good at absorbing a ton of temperature. By doing this, it can quickly change the temperature of the air that passes by it.

If you don’t have enough coolant, then the heat exchanger won’t be able to, well, exchange heat. It means your air will not be as warm as you’d like when it comes out of your vents.

Solution: This might be the easiest solution on our list. All you have to do is top off your coolant levels. You’ll find a coolant reservoir pretty easily when you pop your hood.

Radiator Coolant Inspection
Radiator Coolant Inspection

Problems with the Heater Core

If there’s a clog or obstruction in the tubes of your heater core, it won’t be able to do its job. This is the area where coolant flows through and the air is pumped across. In fact, this is the only part of the HVAC system in your car that heats up the air.

Any general problems within the heater core will result in less-than-desirable air flowing through your vents.

Here are a few symptoms that your heater core might be bad:

  • Inside windows are foggy
  • You’re going through coolant quickly
  • Engine is overheating
  • You smell a sweet, fruity fragrance

Solution: The only way to really fix a heater core is to replace it. It’s a pretty tricky project so we suggest getting a pro involved. Take your car to a mechanic.

Car heater core

Faulty Blower Motor Resistor

The resistor in your blower motor has a big job. It regulates the speed, gives the signal to start spinning and helps air pass through the blower.

The resistor is a simple piece of electronics. If it goes bad, the blower motor will act up or not work at all.

Solution: The solution is to replace the faulty resistor. You can try this project on your own or take it to your local service shop.

Car fuse Box 3
Car fuse Box

Leaking Radiator

The radiator takes care of the coolant and helps it circulate around. The radiator has some other parts like a thermostat and fan to promote the process.

If your radiator is leaking coolant, you won’t have enough to get the job done. The result is a low level of coolant (which we discussed earlier).

Solution: Finding the leak is the hardest part. It’s difficult to look through the radiator and spot the leak, so you might get a mechanic to do it for you.

Close up of green fluorescent coolant liquid leaked out from the
Radiator coolant leak

Blown Fuses

Of course, there’s always the electrical side of things. If fuses or wires are faulty, then the HVAC system won’t get the signal to start pumping warm air.

A blown fuse can be easily replaced on your own. What’s more, they’re not that expensive to replace.

Solution: You can simply replace the fuses on your own. They’re cheap and easy to replace.

Dysfunctional Thermostat

The thermostat does some translation and ensures your car is speaking the same language. After running your car for a while, does the temperature gauge point to “Cold”? This could be an indicator that your thermostat is shot.

The thermostat needs to see a good engine temperature and then signal to your HVAC system that it’s cleared to start pumping coolant and cranking out hot air. A fried thermostat is just like a blown fuse — it doesn’t give the signal that starts the process.

Solution: Similar to a fuse, replacing a thermostat is a quick, inexpensive, and simple fix. You can take care of it on your own.

Engine thermostat 2
Engine thermostat

Clogged or Broken Heater Controls

The heater controls are the knobs, dials, or touchscreen that you use to set the air temp and how hard it blows.

It’s not uncommon, especially in older cars, for these controls to wear down. They’ll get gummed up and eventually stop working.

Another part of the controls is a valve that turns the hot air on and off (a super simple explanation). If the valve is dead, then your vents will either be stuck on AC or heated air.

Solution: The solution is to replace the broken part. Replacing a knob can be really tricky and involve removing pieces of your center console. Replacing the valve is easier, but still takes some patience. If you’re not comfortable doing the job yourself, have a mechanic help.


Water Leaks

If water leaks and gets into somewhere it doesn’t belong, it can freeze. Especially during the winter months. Freezing lines and components will quickly ruin your heater and leave you without warm air.

It’s sometimes tricky to find where the water is leaking from. If you know your way around

Solution: Check your water pump, radiator, and hoses for leaks. If you spot a leak, replace the component. If you can’t spot it, then a mechanic can take care of it.

Repairing car radiator
Inspecting the engine coolant radiator hose

Prevent Breakdowns in the Future

Once you get your heater up and running, the next step is to prevent a breakdown in the future. The easiest and best way to do that is through some maintenance.

Keep a close eye on your coolant level to make sure there are no large dips. If this happens, you can get ahead of the problem and fix it before your heater stops working again.

Moreover, it doesn’t hurt to have a mechanic check out your heating system from time to time. They know what to look for so they can keep your heater pumping warm air all winter. We suggest doing this check right before winter as a way to prepare your car.


We just reviewed some of the top causes of why your car’s heater is not working. We also provided some quick and easy solutions to try out. Hopefully, your car is blowing hot air again in no time. For more car troubleshooting and repair guides, check out the rest of our blog. Make sure you have the right accessories and tools in your garage to have the best car-owning experience.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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