Heater Control Valve


Heater Control Valve

A heater control valve is used to meter the flow of hot engine coolant to a heater core. Then, this hot coolant warms up air either from inside or outside the vehicle that is forced through the heater core. The more hot coolant flows through the control valve, the more heat is released into the surrounding air. This simple principle allows for keeping your passengers warm and protecting your window glasses from ice and condensation.


If you own a newer vehicle, it may not have a heater control valve. Instead of it, your climate control system can utilize a blend door. This is a motor-driven partition that mixes hot and cold air before it comes through your dashboard’s vents. It is operated by the climate control module that relies on the blend door to maintain the chosen temperature inside the passenger compartment. Since such climate control systems don’t feature a heater control valve, the heater system is always on, yet the hot air it provides is either completely or partially restricted.

A bad heater control valve is not a big issue in summer. However, once the outside temperatures reduce to below zero, a bad heater control valve can become a real problem. It may cause an array of problems at nighttime if your windshield is frozen and your heater control valve doesn’t allow hot coolant to enter the heater core. That’s why it is always a good idea to inspect your heater control valve in summer when it is not in use. Here are the warning signs that need your attention:

  • Cold air coming from the vents
  • You can’t turn off the heater
  • Your heating system provides more or less heat that it should
  • Coolant leaks
  • Your temperature gauge shows high readings

Heater control valve troubleshooting and replacement

While a bad heater control valve is synonymous with heating problems in winter, the real danger it can cause is engine overheating due to a coolant leak. If a leaking or improper operating heater control valve is detected it must be replaced as soon as possible to prevent damage to the engine and other related components.

A thorough diagnosis of the entire heating and cooling system is recommended before replacing the valve. Your mechanic should check the valve and all other related parts, including, but not limited to, a cable, a vacuum valve or hose and an electronic device that operates the valve. All hose and lines that come from the valve should also be inspected for wear and damage. If any cracks are detected, a bad hose must be replaced.

Unless you’re a mechanic, we do not recommend you to work on your heating and cooling system yourself. Both diagnosing and replacing processes require an understanding of the climate control system operation. Plus, if your heater control valve is operated by a vacuum-powered system or a climate control unit, its diagnosis and replacement can be tricky and involve special tools and equipment, so it’s better to leave this job to a professional.

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