How to Flush a Heater Core

by Carl Pruit

One of the problems that car owners may experience is when the heater is not heating properly. It can be very uncomfortable for passengers, especially in the winter months. This is actually a very easy problem to fix, requiring just a small amount of your time. The problem is often associated with a clogged heater core and a simple flushing of the unit can have you enjoying a warm and comfortable ride once more.

How to flush a heater core

Locate the heater core of your vehicle by finding the two rubber hoses going into the firewall. Your heater core is inside the firewall, between the engine compartment and the cabin of the vehicle. Detach the two hoses from the heater core valve stems by loosening the spring clamps around the hoses with a screwdriver. Twist hoses back and forth carefully to remove from valve stems and move hoses out of the way.

Run water through one of the valve stems by turning on the garden hose and placing the end of the hose on the valve stem. Flush out the heater core this way until you see clear water coming from the other valve stem. Turn garden hose off.

Replace the two rubber hoses from the engine and secure to valve stems by tightening screw clamps with screwdriver. Be careful not to over-tighten.

Turn car engine on and turn on heater fan to test and verify that heater is working.


  • close Do not spray the water into the heater core or use a spray nozzle, because high water pressure can rupture the heater core.

Items you will need

About the Author

Carl Pruit has been a freelance writer since 2005, specializing in service journalism and travel. His work has appeared on various websites. Born and raised in California, Pruit attended Contra Costa Community College in San Pablo, Calif. and received an associate degree in the administration of justice.

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