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What to Do if Car Heater is Not Working

Omkar Phatak
One of the most common problems discussed on car repair forums is heater failure. Here are the prime causes that may lead to it and explain ways in which you could fix it.
With the onset of the chilling winter weather, it is impossible to travel long distances, without your car heater being in working condition. When you find it to be dysfunctional, especially during winter time, it is as good as having a car breakdown. So it's essential that a such a failure be diagnosed for exact causes and be fixed as soon as possible.

Working Mechanism

You might be under the impression that a car heater is just like the electric or gas heater you use at home. Nothing could be further from the truth. The heat provided by these devices is not generated by the passage of an electric current but by the car engine itself.
The engine generates tremendous amount of heat every second, when it is burning fuel to power your car. This heat needs to be directed away from the engine, as otherwise, it may cause overheating, followed by complete failure.
A coolant is continuously passed around the engine to absorb heat and drive it towards the radiator, where it's radiated away. The heated coolant acts as a source that supplies heat to the car's heater core.
The core is just another radiator, through which the heated coolant is passed. The heat from the core is transported into the car interiors, by a motor-powered fan. Thus, the engine cooling and car heating mechanisms are interlinked with each other and therefore, a malfunctioning in any one, is often linked with the other.


Considering that the heater is linked to the engine coolant system, to diagnose the problem, you may need to check several things. Here are some of the things which should be on your checklist, to fix the heater.

Low Coolant Level

More often than not, the reason for heater breakdown, is a drop in coolant fluid levels. If the volume of the fluid has dropped down, the amount of heat transported will be lesser and subsequently, the car interior won't heat up adequately. To take care of this problem, you must top up the coolant fluid reservoir.

Blown Fuse

The car heater failure may be associated with a malfunctioning of the electrical system associated with it.
A blown fuse, associated with the control valve, may be the cause of heater problems. When this happens, you might notice the heater blowing cold air. Check the car manual to locate the fuse mechanism and check if it's working. In case it's a blown fuse, get it replaced.

Control Valve Failure

The control valve is like a switch which activates or deactivates the flow of heated coolant into the core. If the control valve has stopped functioning, you will have to get it replaced, to restore normal functionality.

Fan Motor Failure

Another reason for the heater failure might be a failed fan motor, which drives the heat radiated by the core, into the car interior. Check if the motor is functional and get it replaced from a repair technician.

Blocked Heater Core

Another chronic problem, that may lead to heater malfunctioning, is blocking of the tubes through which the heated coolant flows. The recommended measure is to go for a replacement.
Run a regular maintenance check on the engine coolant level, to ensure that the cooling and heating mechanisms are both functioning properly. Make it a point to get the heater system checked before the onset of winter, to take care of any potential problems, before they exacerbate further.