Car Heater Stopped Working – Symptoms, Causes & Fixes

It’s cold out there. Even in California, Florida, and Texas, you need a good working defroster for that chilly early morning drive. And if you live up north, a good working car heater is a must-have.

If your car heater stopped working, you have a headache that needs some pills. It can be downright dangerous. Unfortunately, several parameters can cause the car heater not working, making it a bit challenging to track the root cause.

If your car heater stopped working all of a sudden, you need an immediate solution. In this article, an expert from Rx Mechanic will outline the symptoms, causes, and how to fix them. But first, how does a heater core work in a car?

How does a car heater work?

The car heater is an integral system that helps keep the engine cool and the drivers and passengers comfortable in the cabin. In simpler terms, the car heater does not just keep the cabin warm. It also helps the cooling system keep the engine at the normal operating temperature.

You need to know the essential car heating system components to better understand how the heater works.

The heating system works in unison with the cooling system’s thermostat, engine coolant, radiator, water pump, and radiator hoses. When the car engine gets hot, the thermostat opens, allowing cool coolant from the radiator to travel to the engine to keep it cool. As the coolant enters the engine, the engine returns the hot coolant to the radiator via the return hose.

The heat generated by the engine needs to go somewhere, while you need the cabin to be warm. Here’s where the heating system comes into play, making it a win-win situation.

However, a large portion of the heat generated by the engine goes out through the exhaust tailpipes. And the rest returns to the coolant.

The heat from the engine travels from the radiator into the heater core. This means the radiator acts as a heat exchanger. The radiator grants coolant passage to the heater core, and the heater control valves control the coolant passage.

As the hot coolant (engine heat) travels to the heater core, the heat control valves start to warm. When you switch on the heater from the control buttons, the blower motor will force air to pass through the heater core into your cabin, sending hot air inside the car.

What Causes the car heater to stop working?

As with several car system components, several parameters can be the leading culprit. This requires you to examine all the possible causes when diagnosing a fault in the system. Here are the reasons your car heater is blowing warm air, not hot.

Faulty thermostat

Yes, we know that the thermostat is a cooling system component, but it also plays an essential role in the car heating system. If the thermostat fails, it can keep the engine from getting up to the average operating temp. This can prevent the engine from generating enough heat to send to the heater core for heating purposes.

A faulty thermostat can make you beg for warm air when driving on that cozy morning or make you shout, “oh no! My engine is at risk.” You need to diagnose and replace the thermostat in whichever situation you find yourself in.

Low-engine coolant/Antifreeze

This is one of the most common causes and the first to check when the heater isn’t working as it should. Low coolant mostly means there’s a coolant leak somewhere in the system. Regardless of what it means here, enough engine heat will not get into the heater core for heating purposes. 

Leaky radiator

Engine coolant leaks can prevent engine heat from getting to the heater core and cause engine overheating. As a result, you will notice the car heater stopped working and the car overheating. The latter is quite dangerous because it can cause catastrophic engine breakdown if not fixed on time.

Blown fuses or faulty wiring

The heater wiring harness could be broken or shorted. If this occurs, the heater will not activate when you switch on the heater from the cabin.

Faulty HVAC controls

The HVAC controls, knobs, buttons, or haptic feedback touchscreens can break or malfunction. In situations like this, the heater system will not activate when you switch it on.

Faulty blower motor resistor

If your car heater just stopped working, you may have a faulty blower motor resistor. As a result, you will get little or no air inside the cabin.

Lousy heater fan

Even if everything is working properly and engine heat is entering the heater core, the heater fan can become faulty and unable to push the heat into the cabin. If the heater fan in your car stopped working, you might have a shorted wire in the system.

Clogged heater core

This issue is less often than most of the outlined probable causes above. However, it happens not that frequently, but dirt, debris, and particulates can creep into the antifreeze and clog the heater core.

This mainly occurs when the radiator or water passages get rusted or debris creeps in through the radiator and travels to the heater core. This can lead to replacing or unclogging the heater core.

Symptoms of bad car heater

The symptom of a bad car heater is as obvious as one with a purging stomach. You won’t have heat when you turn on the heater. However, there are other signs that show one or more of the heating system components is going out.

No heat

The most common sign of a bad car heater is no heat in the cabin when you switch on the heater. However, several parameters like a clogged heater core, leaky radiator, low coolant, blown fuses, lousy thermostat, faulty blower motor resistor, and broken heater controls can be the culprit.

Sub-par heat in extremely cold weather.

Your heating system may feel okay when driving in mildly cold weather but disappoints you in extremely cold weather conditions. This is an indication of a partially clogged heater core.

This situation shows that enough heat is transferred to the heater core, but the overall heating capacity is reduced due to the partial clogs. A thorough heater core flush is all you need to fix the problem.

Possible engine overheating

While the cooling and heating systems differ, some of the components work together to achieve common ‘heating-cooling’ purposes. By this, some components like the coolant, radiator, and thermostat help in both cooling and heating purposes in a car.

If any of these components go bad or the coolant level is low, it will lead to overheating and also affect the heater.

How do I fix my car heater?

As reiterated above, several factors can cause the car heater to stop working. Some of these are not for inexperienced DIYers. However, we’ll explain how to fix some of the probable causes.

Replace the thermostat

Test the thermostat and ensure it is working properly. If the thermostat is the root cause, replace it and refill the coolant to resolve the problem. This article, Symptoms of a bad thermostat (causes & fixes), will guide you through the testing and replacement procedures. It also provides a visual presentation for better clarification.

Add engine coolant

Park the vehicle safely and allow the engine to cool (about 15 to 25 minutes). After that, open the radiator cap and examine the coolant level. If the coolant is low, top it with a new coolant until it fills to the brim.

Next, check the reservoir tank, ensure the coolant is within the recommended mark, and add more if necessary.

Fix radiator leaks

Examine the radiator for leaks if you detect any leak on it, repair or replace it, depending on how severe it is. You can do this yourself or have a mechanic fix it.

Inspect and replace a bad fuse.

Locate the fuse box in the engine bay and the one underneath the steering wheel. Open the cover and trace the heater fuse by following the instructions on the cover. Once you locate the fuse, pull it out and inspect the metal strip on the two terminals.

If the metal strip is broken, you have a bad fuse, which could be the culprit. Replace the fuse with a new one with the same amperage and see if that solves the problem.

Fix broken control buttons.

If you notice a broken heater control button, replace it and see if that resolves the underlying problem. Search for a Youtube video that demonstrates how to replace broken heater controls for your specific car model.

Unclog heater core

Inspect the heater core and unclog or replace it. We have published a simplified guide on the symptoms of a bad heater core ( causes, how to test, & how to unclog it). Follow that guide religiously to unclog your heater core.

How much does it cost to fix a car heater?

It is likely impossible to accurately estimate the repair cost of a car heater because several factors can be the culprit. However, you can spend as little as $10 or as high as $1,000 to repair a bad car heater.

If the heater core is damaged and needs replacement, it will cost you around $700 to $1,000. On the other hand, if the cause is low engine coolant, you will spend $10 or even lower to fix the problem.

FAQs

What makes a car heater hot?

The car heater collects heat from the engine and sends it into the cabin. Here’s how it works. As the engine warms up, it generates heat and transfers it to the radiator. The radiator sends cool coolant into the engine to keep it running as designed and then exports the heat to the heater core in the form of hot coolant. The heater motor force air through the heater core, sending the heat into the cabin.

Does the car heater work when the engine is off?

Yes, the car heater will work for a while after shutting down the engine before it stops. Remember, the heater uses engine heat, so once you shut off the engine, it stops generating heat to keep it running. But, the heater will continue using the already generated heat until the heater fan dissipates the heat inside the heater core.

Does having the car heater on use fuel?

Yes, the car heater uses some extra gas, but the extra fuel is as small as insignificant or nominal. It is too small to affect gas consumption. In fact, you won’t even imagine it because it is too little to be noticed.

How long should a car heater take to warm up?

The duration differs depending on your engine type and car model. For instance, if you own a late-model four-cylinder engine, it’ll take around 10 to 15 minutes to drive for the heater to warm up and send enough heat into the cabin. But an older car with a four-cylinder engine takes around 5 to 10 minutes.

Is it okay to sleep in car while running?

According to a report from the Ministry Of Health (MOH), sleeping in a car while running is not okay, even if you roll down the windows. This act will entrap air in circulation, causing oxygen reduction and increased carbon monoxide. If you decide to sleep in the car and turn on the AC while driving, it’ll lead to a life-threatening situation due to carbon monoxide poisoning.

Can you drive a car without a heater?

Absolutely yes. Your car heater cannot stop the vehicle from moving. It only provides heat into the cabin to keep you warm, especially when driving in cozy weather. However, do not ignore the signs of a bad heater.

It could mean you have a low coolant level, a lousy thermostat, or a leaky radiator. Any of these issues can cause engine overheating. Of course, you won’t want that to happen.

Does turning off the heat in car save gas?

As explained above, the car heater uses extra gas. So, turning it off will save gas as well. However, you may not even notice it because the extra gas is too small.

How many hours does it take to replace a heater core?

Heater core replacement is one of the tedious heating system replacement jobs. And that shows why the replacement costs around $700 to $1,000, depending on your car and location, with the replacement part around $100 to $300. On average, replacing a heater core takes around 4 to 6 hours. However, you may spend between 6 to 8 hours on the job if you’re an amateur.

Final Words

A car heater is essential for early morning driving anywhere in America and some other parts of the world. It is essential for those living around the north. We‘ve outlined the probable causes of a car heater stopped working, the symptoms, and also explained how to fix the problem.

If your car heater stops working, first examine the coolant level and the thermostat and see if any of them is the culprit. If any of them is the cause, fix it following the instructions above.

But if you tracked the leading cause to any other possible causes, have a mechanic fix it unless you’re an experienced DIYer.