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Why is my car heater blowing cold air?

Charlotte Phillips, 23 days ago

3 min read

  • Advice
  • why
Car heater

WhoCanFixMyCar explores the reasons why your car heater may blow cold air, including the common causes and the average cost to get your heater repaired.

Why is my car heater not working?

How does your car heater work?

What are the signs of a broken car heater core?

How much does it cost to repair your car heater?


Why is my car heater not working?

There are a few different potential reasons why the heater may have stopped blowing hot air in your car:

Top reasons your car radiator is blowing cold air

  • Low coolant level

  • A clog in the cooling system

  • Dirty air filter

  • Fault with the thermostat

Low coolant level

If your coolant level is too low, your heater will blow cold air into your car.

Coolant is usually a mixture of water and antifreeze, and works not only to stop the engine from overheating, but also by helping the heating system to produce warm air.

Clog in the heater core

Additionally, if your coolant level is correct and your car is still blowing cold air, there could be a problem with the heater core being either clogged or leaking.

Dirty air filter

A dirty air filter will impact the efficiency of the heating system in your car. When your car’s filter is clogged, it won’t properly allow air to flow through the heater core, which is why you might notice cool air.

A fault with the thermostat

The thermostat in your car is a valve, and if this valve gets stuck or develops a fault, it could begin blowing cold air that should be warm.


How does a car heater work?

The heating in your car works in a fairly simple way:

  • Your vehicle’s engine begins to heat the coolant to a high temperature

  • The coolant then moves through the heater core, which acts like a small radiator

  • This air then exits the heater core having been warmed up, producing hot air in the cabin


What are the signs of a broken car heater core?

There are a few tell-tale signs to look out for that your car’s heater core is going bad: 

1. Sweet smell in the cabin 

Noticing a sweet smell lingering in the cabin could indicate that the heater core is leaking, and as a result blowing the scent of engine coolant through your vents. Coolant is said to have a sweet and musty smell.

2. Recurring coolant loss

If your coolant seems to be constantly running low after topping it up, there’s likely to be a coolant leak in the heater core. This can make your engine overheat and cause serious damage, so it’s important to get this checked out by a professional as soon as possible.

3. Cold air blowing from vent

A more obvious one - noticing that cool air has began to blow from your vents is a clear indicator that something is going wrong with your heater core.

4. Fog inside the cabin

When your heater core stops functioning properly, this can prevent your defrosters from working resulting in a fog building up inside the cabin.


How much does it cost to repair your car heater?

Luckily, if your car heater stops working properly, it’s a relatively inexpensive component to fix.

While prices can vary, the average quote for a car heater repair booked through WhoCanFixMyCar is £62.56.


If you think you might need your car heating repaired, there are a number of garages in our network who can do this for you. Simply enter your registration and postcode on the homepage to get a quote from a local specialist.