A heater matrix is a small box located behind the dashboard of the vehicle and is built in a similar way to a radiator, and has hot water/coolant running through it, but instead of radiating heat it has air passed over it by a fan and the air is heated. When the driver turns the heater controls in the vehicle, the heater matrix operates and the passenger compartment of the vehicle is heated.
The most common reason for heater matrix damage is blockage. These are difficult to unblock, and it is often easier to replace the heater matrix rather than attempt to have it unblocked.
Signs that the heater matrix is damaged can include a lack of heating in the vehicle, or finding coolant in the front passenger side footwell of the vehicle. If you turn the controls and only receive cold air, it is possible that you have an issue with coolant and the heater matrix should be checked. You may also notice a fine mist of coolant on your windscreen if a heater matrix fails. This is caused by the coolant being found in the ventilation system.