Photo of heater and climate controls on a car dashboard

When Your Car Heater Stops Working


With the weather getting colder, we’re using our car heaters more and more. If your vehicle’s heater isn’t working, this can be dangerous. Depending on how cold it is, too much exposure to low temperatures isn’t good for you or your fellow passengers. It’s also dangerous if your windows cannot properly defrost.

What causes a car’s heater to stop working? Heating systems are made up of many different components. There are a number of areas that could be malfunctioning and stopping the heat from getting to you. Below are some of the most common things that can cause a broken car heater.

Problems with the Antifreeze

Antifreeze is a mixture that helps to regulate your engine’s temperature. Antifreeze also moves heat produced by the engine to your car’s heater core. This is where the heat in your car’s cabin comes from.

If the antifreeze becomes contaminated, or if the levels are too low, your engine may overheat. The antifreeze will also be unable to properly flow through the heater core, causing your car’s heater to stop working.

If your vehicle’s heater does not put out heat after 10 to 15 minutes, it may mean your antifreeze is low. If you find this happening shortly after refilling your antifreeze, there is likely a leak. It’s best to have your vehicle checked by an auto repair expert, like the ones at Restored Auto, LLC. Continuing to refill the antifreeze will not fix any leaks that may be present in your vehicle.

Problems with the Heater Core

Your vehicle’s heater core functions similarly to your vehicle’s radiator. The heat comes off of antifreeze that’s been heated by the engine. While the radiator disperses that hot air out of your vehicle, the heater core blows it into the cabin or onto the windows.

Heater cores have lots of tubes that can leak or become clogged. If your antifreeze is contaminated, this can cause a blockage in your heater core. If your vehicle smells sweet like antifreeze, if your windows become partially fogged, or if you notice puddles under your dashboard, you may have a clogged heater core.

Problems with the Heater Control Valve

Not all vehicles have these, but heater control valves determine the direction of the antifreeze. Air conditioning will divert antifreeze away from the heater core, allowing cold air to come through instead. If this valve is faulty, it may cause leaks or it may get stuck open or shut. If it is stuck shut, you will feel cold air blow when you turn on the heat.

Problems with the Thermostat

The thermostat works similarly to the heater control valve. It directs the flow of antifreeze and helps regulate the temperature of your car’s engine. If the thermostat is damaged, it may get stuck open or stuck shut.

If the thermostat is stuck open, it disrupts the flow of antifreeze, which will in turn disrupt the temperature of your engine. If this is happening, you’ll notice a decrease in engine performance.

If the thermostat is stuck shut, the antifreeze will not be able to circulate properly and you won’t feel heat in the cabin of your car.

Problems with the Cabin Air Filter

Your car’s cabin air filter helps to stop dust and other debris from getting into your car’s cabin. When working properly, the cabin air filter will collect dust and, over time, it will clog up. You should have your filter replaced on a regular basis, or this natural clogging will reduce the airflow from both your heater and air conditioner. It’s fairly easy to tell if this is what is preventing your car from heating up. Clogged cabin air filters prevent all air from coming through, whether you have the AC or the heat turned on.

Problems with the Heater Fan

Heat is captured from hot antifreeze inside of your vehicle’s heater core. It is then moved from the heater core and into the car cabin via the heater fan (sometimes referred to as a blower or blower fan). This fan can stop working if has been damaged or if a fuse has blown in your vehicle. If a broken heater fan is to blame for no heat in your car, you’ll know because you won’t feel or hear air blowing into your cabin.

Problems with the Blend Door

Newer vehicles sometimes use what’s called a blend door in the heater and air conditioning system. Rather than separate doors, a blend door switches between airflow from the heater core or from the AC’s evaporator. Unlike older cars with one heating system, a lot of newer cars have dual climate control. The blend doors also control the defrost, the floor vent and the main cabin vents. With all of these different parts, there are a lot of areas that can get stuck or stop working. If the blend door sticks open on the AC side, heat will not flow out from the heater core and the car will not warm up.

In Conclusion

As you can see, there are a number of causes that result in no heat. If you have a broken heater, give us a call! Restored Auto, LLC can diagnose the problem with your car’s heater and get it back up and running for you. It’s important to keep your heater in proper working order so you can keep warm and clear your windows for better visibility while driving. Don’t hesitate to get your heater repaired. Call Restored Auto, LLC today!