Heater problems

Heater issues can vary depending on the complexity of the system. A classic Defender or Series heater is simpler compared with, say, a Range Rover or Discovery which may use air conditioning, blend motors and electronic controls. Such systems can mean electrical issues raise their head, but in terms of a lack of heat, the main causes are the same, regardless. All you need to do is check the symptom.

Firstly, lack of heat. This could be down to low coolant level, in which case check for leaks, repair them, and refill. If a heater blows hot air on the move but cold air at idle, then there is likely to be an air lock in the heater, in which the heater matrix traps air – it’s a particular problem for 1994-onward Range Rover Classics (soft dash). You may also notice gurgling noises from the heater as you accelerate, which is a sure sign of air in the matrix. Cure that by following the correct filling procedure. But some people swear by raising the front of the car while filling the system, to help bleed air out on Range Rover Classic and Discovery 1 and 2 (all engines) models. A total lack of heat could be a failed thermostat in the engine’s cooling system. On more complex systems, all electrical issues begin with checking fuses. Blower motors, heater resistors and blend motors can, and do, fail.

If the coolant level is correct and there are no air locks, yet heater performance is still lacklustre, then the heater matrix may be blocked. Being off the main flow, with smaller internal spaces than the engine pipework, they can collect debris which, over time restricts the flow through the matrix. A lower flow means less heat is transferred, so less hot air flows into the car. The way to check this is to feel the two hoses that feed the heater matrix. If one is hot and the other cold, you either have an air lock, or a blocked matrix.