Your car heating consists of a heater core, a fan, the coolant system, a thermostat, a selection of tubing and pipes, as well as its dashboard controls. If your heater isn’t operating as it should, then one or more of these components isn’t doing its job properly.

Any of the pipes or heater core could be clogged or blocked; there could be a problem with the power supply or electrical components, or you might even have a leak in the cooling system. To diagnose exactly what the problem is, you may need a mechanic to take a look under the bonnet.

Why doesn’t my car heater work?

The first thing to check is your coolant. It’s one of the most common causes of a failing car heater and the most easily rectified. If your coolant level is where it should be, then it could be one of a wide range of alternative issues: electrical or mechanical.

Remember—safety first! Always let the car and its components cool down before examining a hot system for faults. You don’t need a trip to A&E as well as one to the garage.

What are the common causes of a broken car heater?

There’s a faulty valve, switch or thermostat

Risk level – Medium

What to do – Find the faulty component and replace it.

Faulty thermostats are the most common reason for a failing car heater. The thermostat is responsible for ensuring the engine operates at the correct temperature and using the coolant to adjust the levels. If it’s faulty or broken, it affects the heating system as well as your car’s performance.

There are also a few valves that could block or stick over time, and after years of regular use, the controls on your dashboard might have finally jammed or developed faulty connections.

You’ve run out of engine coolant

Risk level – High

What to do Top up your coolant straight away, and then check for leaks.

When the coolant level drops below a certain point, the hot fluid can’t find its way into the heater core, resulting in a cool cabin. It’s one of the simplest problems to rectify, as most motoring depots will carry pre-mixed coolant for every make and model. However, driving with an overheating engine is dangerous, so don’t take any risks if your temperature gauge is heading into the red.

There could be a blockage in your pipes or heater core

Risk level – Medium

What to do – Replace or refurbish your heater core.

It’s less likely to be a heater core issue than many other causes, but it still happens. If debris or particulates infiltrate your coolant system, they can clog the core, preventing the heat from dissipating.

Your heater fan has broken

Risk level – Low

What to do – Replace the fan if it can’t be repaired easily.

If your heater fan isn’t moving any air, then you’re incredibly unlikely to feel the benefit of the heated air within the system.

There’s an issue with the power supply

Risk level – Low

What to do – Check the fuses and power distribution.

It could be a blown fuse, faulty wiring, or a short in the system. Whichever your problem, they’ll all prevent the fan from powering up and delivering the hot air you need.

How much does it cost to fix a car heater?

It all depends on what’s causing the problem. You could expect to pay anywhere between £250 and £550 for most electrical or mechanical issues—or around a tenner, if your car only needs topping up with coolant.