It's no fun getting into your car on a frosty winter's morning only to find the car heater not blowing hot air. It's almost as unpleasant to have a car heater that's not giving out enough heat.
If you’re wondering why is my car heater not working, you’re almost certainly wondering how easy it will be to fix.
Luckily, if you find your car heater not working properly, unlike many systems on the modern motor car, heating systems are more or less built around the same design as they were 20 years ago - which is ultimately a basic one.
That said, there are multiple reasons why your car heater could be busted - and working out which one it is can be tricky.
Equally as frustrating as a car heater not working, is facing problems with your car air conditioning not working properly.
How easy is it to fix car heater problems?
If the problem as to why your car heater is not working is simple - and you can diagnose it - then it's possible to fix it yourself.
But some issues are more complex, meaning that to fix the problem with the heating not working in your car, a visit to your local garage is necessary.
For example, a car heater that does not work at all could be suffering from a broken blower motor or switch, while a car heater blowing cold air could be affected by low coolant or a clogged up heater core.
With luck, any issues you have with your car heater not working will become evident in warmer months, so you can fix them before winter sets in.
Common reasons car heater isn't working, and potential solutions
In most cases, car heater issues fall under two headings:
1. Car heater systems that blow air
If you find that your car heater system is blowing air but that your car is not heating up:
- There could be a blockage or other problem stopping heated antifreeze from moving through the heater core component.
- A valve or switch could be faulty, or the heater core could be a clogged.
- Wait until the engine has cooled down and check the coolant level, topping it up if needed.
2. Car heater systems that simply don't work at all
If your car heater is not working at all, you're looking at:
- a faulty blower motor, or
- an issue stopping power from reaching the blower motor.
In order to fix this, you might have to prise open the heater box, or perhaps even lift a section of the dashboard to access the blower.
My car heater has suddenly started to blow cold: what should I do?
Is your car heater blowing cold air instead of hot air?
If you feel the chill of cold air in your car, even after the engine has been running for some time (and the system is set to hot), then the following issues are likely causes as to why the car heater is not blowing hot air:
- Heater core is clogged
- Coolant is low
- Blend door is jammed/faulty
- Heater valve is jammed/faulty
- A switch or linkage is faulty
How to fix a car heater:
Check your coolant levels
First of all, check the coolant level - but wait until the engine is completely cool, or you could be burned.
- If you discover coolant is low, there may an insufficient amount moving through your heater core. - While in the short term, topping up your coolant could address the issue, providing a quick fix for no heat in the car, the fact it was low in the first place indicates another, more serious problem;
- It may mean a hose or gasket is leaking, or worse,
- that you have been burning the coolant itself, strongly suggesting a blown gasket.
- If a refractometer indicates the pH is off, it’s likely a component has suffered corrosion and begun to leak.
- Miscoloured coolant, or coolant that smells off, also suggests an issue.
In the case of having sufficient coolant, you can switch on your engine and let it heat up, before checking the temperature at the point where the heater core and hoses connect.
How do you check the car coolant temperature?
It is best to use an infra-red thermometer to check the car coolant temperature, since it does not require any contact.
If you discover one of the hoses is the same temperature as the coolant but that the other hose is cold, it is likely your heater core has become clogged, which will explain why your car heating is not working as it should.
If your car has a valve in the affected hose, you should check to see if it has got stuck.
How to work out if my blend door is jammed or otherwise malfunctioning?
Turn off your car heating and listen for the blend door moving.
If you can't hear it move, you may be looking at:
- an issue with the thermostat switch (if your car has one);
- a jammed hinge on your blend door;
- or a linkage/wiring fault.
Faulty blower motor?
If your car heater is not blowing hot air, then you probably have a faulty blower motor, although there's an outside chance there could be another explanation.
How do you check your car blower motor?
To check the car blower motor you will need some basic diagnostics tools, which will tell you if power is coming through. You will need direct access to the motor to do this.
You might also be facing a faulty blower resistor; relay; or switch.
Each car is different, so how you work out the problem will depend on your model. Check your owner’s manual for more information.
Power reaching the blower motor but heater not working in car?
If you believe power is reaching the motor, there are several possible reasons as to why your heater is not working in your car:
- The motor has burnt out.
- The motor has been clogged up with debris to the point that it cannot work.
- There is rust and/or damaged wires.
In the case that power is going to the motor, you should check the blower fuse, resistor, relay and switch.
Changing the blower fuse
If you think the cause for your car heating not working is related to the blower fuse, be sure to replace it with one of the same amperage.
The fuse may have blown due to age, or it may suggest an underlying problem. If the replacement fuse (of the same amperage) does not blow, you may well have identified the problem.
Do not be tempted to replace the fuse with one of a higher amperage to keep it from blowing again.
Frequently asked questions
How does a car heater work?
Most car heater systems - i.e. ones that come with water-cooled engines - harness the coolant to heat the car interior.
The coolant at this point is inappropriately named since it is extremely hot.
This fluid is pushed through the heater core, which is essentially a mini radiator. In turn, air is pushed through the heater core, which results in your cabin being filled with delightfully warm air - or at least, that’s what should happen.
Why is my antifreeze passing through my heater core?
If antifreeze is passing through your heater core there could be dirt or other matter stuck in the heater box, or the blend door is jammed/faulty.
Should I get a garage to repair my car heater?
For those without the necessary skills, mechanical aptitude or motivation, and for those who are simply too busy with other things, it may make a lot of sense to let your local garage fix the problem with your car heater, rather than trying to work out for yourself why your car heater isn’t working, and trying to fix yourself.
Car heater not working: Will it fail MOT?
If your car heater is not working, you may well be wondering if this will cause your vehicle to fail the MOT.
Whilst a broken car heater can be inconvenient (and cold!), it is not one of the core components checked as part of an MOT.
Click here for a full list of car parts checked at an MOT.