The heater control valve (also known as the hot water valve) is the component that collects some of the hot coolant from your engine and diverts it to the heater core. As air also passes through the heater core, it is warmed up by the hot coolant and the warm air is distributed throughout your vehicle through the air vents. The heater control valve is the component that is adjusted when turn the heat control knob on your dashboard or center console–allowing more or less warm air to pass through depending on the setting. This same heat is used to clear your windshield(s) of ice and snow.
Note that not all vehicles have a heater control valve. Some models use a blend door instead–a motorized door-like component that separates the heating and AC systems. The blend door opens and moves to balance the amount of warm and cool air that travels out of the air vents based on the input from the heat/AC control knob. With a blend door system, the heat is always on, even when just using the AC, so a heater control valve is not necessary.
Signs of a bad heater control valve
Driving with a malfunctioning heater control valve can present major issues. Since it is a part of your vehicle’s climate control system, it may cause problems in keeping your windows clear which can affect your visibility. You will also find it hard to control the temperature inside of the car, whether it is too hot or too cold. Below are the signs of a bad heater control valve:
- No heat coming out
- Heat always on and cannot be turned down
- Heat output changes with no changes in the heat setting
- Temperature gauge reads hot
- Low coolant level
- Coolant leak
Heater control valve maintenance
Many issues with a heater control valve can stem from a coolant leak, which can cause your engine to overheat–posing a serious risk of expensive engine damage. It is important to get your vehicle inspected by a car care professional right away if you notice any of the above signs. Do not attempt to fix the heater control valve yourself unless you have extensive professional-level car repair knowledg–these systems are complex and are often built around electronic computer controls, requiring specialized tools and knowledge to fix.