Why isn't my car heater working?
Making sure your car heater is working in the winter is an important safety precaution. (Photo by Steve Mitchell)
The morning commute can be stressful.
But if your car heater suddenly stops working in the middle of winter, it can make it downright miserable.
Not only would the inside of your car feel like an ice box, but a broken heater can prevent your defroster from blowing warm air to your windshield to eliminate ice and fog, which can pose a hazard while driving. Not having a working heater in your vehicle could even become a dire situation, if you end up stranded.
Causes of a car heater breakdown
Ken Mattson, owner of highly rated Len’s Automotive in Bellevue, Wash., says a car heater can stop working for a number of reasons, including:
•A low antifreeze/water level in the radiator due to a leak in the cooling system.
•A bad thermostat that isn’t allowing the engine to properly warm up.
•A blower fan that isn’t working properly.
•Coolant that contains rust particles or becomes otherwise contaminated and is blocking the heating core from circulating air into the cabin properly.
“Depending on the problem, different types of repairs would be required,” Mattson says. “There really isn’t a heater unit, like a furnace in your house, that you can just replace. It is more a combination of different things that provide heat into the vehicle. It’s very difficult to give a cost due to the wide variety of possible problems.”
One of the most important components, the heater core, which acts like a small radiator, passes the hot air from under the dashboard into the vehicle. They can cost several hundred dollars to replace.
“I often describe a heater core as a part that is placed on a workbench, and the car is built around it,” says Robert Ramsey, owner of highly rated Ramsey’s Service Center in Drexel Hill, Pa. “To replace a heater core, it sometimes takes a day or more to repair.”
Most heating-related repairs range from $300 to $1,000, he says, but it’s difficult to pinpoint an exact number because of the variety of problems that exist.
A decrease in the coolant level or a leak in the coolant system is one of the more common problems, Mattson says. Coolant doesn’t evaporate on its own.
“Topping it off may help in the short term, but it’s an indication of a deeper problem and should be checked out,” Mattson says. “You shouldn’t have to add anything at all if everything is working well. It can damage the motor if there is low heat [from too little coolant].”
Ramsey adds that a leak could be as simple as a loose hose clamp, or a major problem like a leaking engine cylinder head gasket, which can cause serious damage to the engine and cost several hundred dollars to replace.
Maintenance can prevent car heater failure
Several components make up the heating system, so unless you have experience with car maintenance, it’s best to have a reputable auto mechanic diagnose the problem.
In general terms, a heating system works when the vehicle receives heat from the engine’s coolant system. Once the engine reaches its operating temperature — controlled by the thermostat — it heats up the coolant and water mixture, passes it through hoses and valves and into the heating core, which resembles a miniature radiator.
A blower fan then pushes the warm air from the heating core through the cabin filter and into the vehicle.
The No. 1 tip, mechanics say, is to have a mechanic asses your car heater regularly by having a mechanic checking the coolant level and the other components. However, Ramsey adds that coolant in newer vehicles may not need service until 60,000 to 100,000 miles, and heating problems usually don’t occur on newer vehicles.
“Maintaining your vehicle’s cooling system helps prevent a heater failure,” Ramsey says. “Checking hoses, belts and keeping the coolant clean and filled are simple basic maintenance that will help keep it working.”
Editor's note: This is an updated version of an article originally posted on Dec. 11, 2013.