In the colder months, our car heaters are a godsend. The last thing you'd want on a frosty winter morning is to find that your car heater is having issues, or not working at all. Aside from keeping us warm, they're also pretty useful for demisting and defrosting windscreens.
Below, we explain how a car heater works, why it may not be working and what you can do about it.
Read more useful advice on driving during winter.
In this article
How does a car heater work?
Most car heaters use coolant to warm up the interior of the vehicle. Here’s how it works:
- The vehicle engine heats the coolant to a very high temperature.
- The coolant is pushed through the heater core (which acts like a mini-radiator).
- Air is pushed through the heater core, resulting in hot air blowing into the car.
Often when you first turn the heating on, you’ll notice the air feels cold for a few minutes – this is because the engine needs a little time to warm up and heat the coolant.
Reasons why your car heater isn't working properly
If the heating system isn’t working at all (no hot or cold air is being blown into the car), this is likely due to a faulty blower motor or an issue stopping power from reaching the blower motor, but that's not the only possible reason.
In general, car heater issues can be caused by the following:
- Low antifreeze
If your antifreeze has gotten too low, it means there won’t be enough hot liquid in the heater core, resulting in cold air. You should top up the coolant to the appropriate level and then check to see if the heating is working again.
- Damaged wiring
All in all a damaged wire wouldn’t be the worst outcome as it’s a fairly simple fix, but if your car heater is unresponsive then it’s possible that a short-circuited wire or blown fuse is the culprit.
- Faulty heater fan
It’s possible that your car heater is working, but only until the hot liquid reaches the heater core. If the heater fan itself is broken, then it won’t be able to blow heat into the interior of the car. This could be down to a mechanical failure or electrical problem.
- A faulty or damaged thermostat
One of the most common reasons for car heaters not working, a faulty or damaged thermostat could actually lead to worse problems with your car. For example, if the thermostat corrodes or ages enough, it can get stuck closed meaning there’s no coolant reaching the radiator. With no coolant in the radiator, your engine will overheat, causing potentially critical damage.
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Why is my car heater blowing out cold air when the engine is on?
If you’re only getting cool air when your heating is on, it could indicate a problem.
First things first, make sure you’ve set the system to hot. And let the engine run for a few minutes to give it time to heat up the coolant.
If you’re still getting cool air, then there are a few reasons this might be happening. The most common reasons are:
How to fix a car heater
The first thing to do if you’re having issues with your car heater is to check your engine coolant. Make sure to do this when your engine has cooled down to avoid being burned.
Low engine coolant can be a sign of a leak or other issue in the system so you should also get your vehicle checked by a professional to make sure there are no further problems.
If there is enough engine coolant but the heating still isn’t working, you’ll need to take your car to a garage so an experienced mechanic can diagnose and fix the issue.
How much does it cost to fix a car heater?
The costs involved in fixing a car heater can depend on the problem and what needs replaced or mended.
A full replacement of your heater core can be expensive due to the labour involved, costing upwards of £1,000 for parts and labour.
Find out what’s causing your car’s heating problems with Smart Care.
How does the heater in an electric car work?
Unlike internal combustion engine vehicles, the motor for electric vehicles doesn’t create heat as a by-product of running. This means EVs need another way to heat up the car.
Most modern EVs use a heat pump, which takes thermal energy from outside air and compresses it before releasing the heat inside.
An EV’s heating system does rely on power from the traction battery, which used to result in the range of electric cars being much shorter during winter. But with modern EVs, the heat pumps are very efficient so this is no longer an issue.
Plus, one of the benefits of driving an EV during winter is preconditioning – this means you can pre-heat or pre-cool your car before you start your journey.
This handy feature means you can warm up and defrost your car in the morning while it’s still charging, so it’s ready for you when you want to drive it and there’s no impact on the battery charge.
Read our guide to maintenance and repair for electric cars.
Will I fail my MOT if the car heater is not working?
While a broken car heater is far from ideal, it won't cause you to fail your MOT. This is because it's not one of the main checks done as part of the test.
FAQS
How often should I flush my coolant?
If it's not specified in your car manual, it's widely recommended that you flush your coolant every 5 years or 100,000 miles – whichever one comes first.
Does the heater in my car have a fuse?
It depends on the design of your specific car, but it's possible that your blower motor has a fuse. The blower motor is what powers the fan on your car heater.
Is there a way to heat my car without a heater?
There are several techniques you can try to heat up your car even without using the built-in heating system (if you'd like to try and save on fuel etc.). These include:
- Starting up the engine early, 15-20 mins before you plan to set off
- Buying a small portable car heater
- Buy heated seat covers
- Park under shelter if possible
- Consider insulating your car windows
Why does my car heater only work on high?
If your car heater only seems to work by blowing air while on the highest setting, then it's likely that you have a problem with the resistor motor – which will likely need replacing.