Is your car’s cabin chilly despite turning on the heater?
Your car heater not working could likely be due to a broken thermostat or a clogged heater core.
Wondering how you can identify the problematic component?
Let’s understand the common causes in detail and explore the steps to diagnose a faulty heater. We’ll also check out some ways to fix the issue.
This Article Contains:
- 12 Common Reasons for a Car Heater Not Working
- How to Diagnose a Broken Car Heater
- How to Fix Your Broken Car Heater: A General Know-How
- How Much Does a Car Heater Repair Cost?
- 3 Car Heater FAQs
12 Common Reasons for a Car Heater Not Working
Here’s why your car heater could be malfunctioning:
1. Low Coolant Level
Normally, your car’s heater core transfers the heat from the coolant (glycol and water, also called antifreeze) to the air to warm the cabin.
However, a cracked radiator hose or a broken water pump can leak the engine coolant, reducing its quantity. If there’s insufficient coolant to absorb the engine heat, your car’s vents will eventually blow only cold air.
2. Contaminated Coolant
Coolant helps prevent engine overheating and breakdowns. However, dirt and grime that gradually enter the system can contaminate it.
This impure coolant can potentially harm the water pump and radiator, preventing your heating system from functioning properly.
3. Broken Thermostat
The thermostat opens to release coolant when the engine reaches an operating temperature threshold (180°F – 195°F).
But if the thermostat breaks or corrodes, it can get stuck open or closed. When the thermostat is stuck closed, it prevents the coolant from absorbing the heat. This means no hot coolant reaches the heater core to warm up the air.
4. Air in the Cooling System
Air bubbles can enter the system during an antifreeze refill, coolant leak, or through a faulty radiator. Air in the cooling system can disrupt the coolant flow, preventing the hot coolant from reaching the core.
5. Clogged Heater Core
The heater core transfers heat from the coolant to warm up the air. Then, the heater fan pushes the hot air into the cabin.
Unfortunately, the heater core’s tubing can get clogged with old, contaminated antifreeze or debris. When this accumulation increases, the hot coolant can’t flow through the tubes to heat up the air.
6. Jammed Blend Door
Your car’s heating system contains a flap called the “blend door,” which allows hot air from the heater core to enter the cabin.
When it’s blocked, cool air bypasses the heater core and enters the cabin unheated. This happens due to debris build-up or blend door actuator problems, causing your car heater to blow cold air instead.
7. Broken Heating Controls
Two issues that cause your heater to blow cold air include:
- Broken or jammed heating control buttons
- A malfunctioning heater control valve
The heater control valve adjusts the amount of hot coolant flowing to the heater core. If it’s not working, there may not be enough coolant to heat the air that blows into the cabin.
8. Clogged Cabin Air Filter
The cabin air filter prevents dust and debris from entering the vents.
Over time, contaminants build up and eventually clog the filter. A clogged filter restricts the airflow over the heater core, and you’ll notice that the heater isn’t working at all.
9. Damaged Water Pump
A damaged water pump results in your heater not blowing hot air, as it can’t create enough pressure to circulate the engine coolant through the system. As a result, insufficient hot coolant reaches the heater core, causing the heater to blow cold air.
10. Blower Fan Issues
The blower fan (also called an air conditioning or heater fan) pushes warm air from the heater core into the cabin vents. But problems like a blown fuse, damaged blower motor resistor, or broken blade can stop the fan from working.
11. Radiator Problems
The radiator usually cools down the hot coolant by exchanging the fluid’s heat with the outside air.
However, issues like a broken radiator cap, leaking hoses, and blockages can prevent it from delivering hot coolant to the heater core. This reduces pressure inside the engine’s cooling system, and the heater blows cold air into the cabin.
12. Electrical Problems
Electrical issues, such as short wiring and burnt fuses, can prevent the flow of electricity needed for the car heater to function.
Now that we’ve looked at the causes of a car heater blowing cold air, let’s see how to identify the root problem.
How to Diagnose a Broken Car Heater
Determining which part of your car’s heating system is creating trouble requires access to multiple components in the engine bay. You’ll need experience and thorough knowledge of a car engine to perform the task. If you find it overwhelming, it’s better to let an expert handle it.
To identify the issue, a mechanic would:
- Inspect the coolant level and quality: They’ll check the coolant reservoir for leaks and ensure the coolant reaches the guide mark. They’ll also use a coolant tester to check if it’s discolored (dirty coolant turns brown), indicating contamination or leakage in the system.
- Check the engine temperature: The mechanic will use an infrared thermometer to verify if the engine temperature is within the normal range of 190°F and 220°F (88°C – 104°C). If outside the normal operating temperature, there’s likely a faulty thermostat.
- Inspect the heater core: The mechanic will open the heater box and look for signs of a faulty heater core. If it’s clogged, they’ll need to flush it with air or water.
- Evaluate the water pump: They’ll check the coolant flow through the water pump. Poor or no coolant flow indicates a worn seal or a blown gasket, which causes the pump to leak.
- Assess the blower fan: If the air conditioning fan doesn’t engage even when the fan speed is at maximum, it’s likely an electrical issue. Using a multimeter, they’ll locate the problematic component.
- Inspect the blend door: If the blend door is blocked, clearing the debris would likely fix the issue.
- Assess the heater control buttons and control valve: The mechanic would engage the heater controls and replace them if broken or jammed.
After the inspection, once the automotive mechanic has identified the problem, they’ll proceed to resolve it.
Let’s see how.
How to Fix Your Broken Car Heater: A General Know-How
Here are some common ways a mechanic would fix the heating system:
A. Refill the Coolant
If the coolant level in your car is low, the auto repair mechanic will:
- Switch off the car and let it cool completely.
- Access the radiator and coolant reservoir and check the coolant level.
- Remove the radiator cap, place a funnel in the opening, and refill it up to the guide mark on the reservoir.
- Start the car to check if the car is overheating.
B. Replace the Faulty Thermostat
In case a broken or corroded thermostat needs replacing, the mechanic will:
- Engage the parking brake and use jack stands to lift the front end of the car.
- Open the hood to access the thermostat at the base of the radiator (between the heater core and the main hose).
- Detach the radiator hose at the base to drain the coolant system.
- Remove the faulty thermostat and install a new one in its place.
- Reattach the hose and refill the coolant.
C. Clean or Flush the Cooling System
If there are signs of debris or air bubbles in the system, the mechanic will perform the following steps to flush them out:
- Switch off the car and let it cool completely.
- Park the car and raise the front end using jack stands.
- Open the hood to access the cooling and heating system.
- Drain and refill the coolant using a vacuum coolant filler to flush the air and dirt from the engine’s cooling system.
Next, let’s look at how much these repairs will cost you.
How Much Does a Car Heater Repair Cost?
Repair and replacement costs depend on the various parts of your car’s heating system as well as your make and model.
Here are some cost estimates (including parts and labor):
- Coolant flush: $100 to $150
- Fan blower motor: $330 to $355
- Blend door: $340 to $400
- Heater control valve: $470 to $500
- Thermostat: $500 to $540
- Water pump: $600 to $1,000
- Radiator: $200 to $1,200
- Heater core: $1,000 to $1,340
Curious to know more about car heaters?
Check out the common queries car owners have.
3 Car Heater FAQs
Here are answers to some questions related to heater issues:
1. How Does a Car Heater Work?
Most cars with a heating system use hot coolant to warm up the cabin. When you turn on the heater, the control valve releases the hot coolant. The radiator hose then carries this coolant to the heater core. Here, the coolant flows through the core’s fins, where a fan blows air over them.
As the fan blows, the heat transfers from the hot coolant to the air, making it warm. Eventually, this warm air makes its way to the cabin through the HVAC ducts and vents.
2. Do Car Heater Problems Need Urgent Attention?
Yes, you should take your car to an automotive mechanic if there’s no heat despite turning on the heater. This is especially necessary if you drive in freezing temperatures.
Without a functioning heater, your car’s interior will remain cold in frigid weather, making your drive uncomfortable. The heater also helps defrost and defog the windows. Without it, visibility can be severely impaired, which is a safety hazard.
Moreover, if you don’t fix the root cause, issues like a coolant leak, system blockage, and faulty blower motor can cause overheating and damage to various parts. This can result in high engine repair costs.
3. How to Prevent a Car Heater Problem?
To avoid car heater issues:
- Schedule regular maintenance of the thermostat, blower fan, and other heating system parts once a year before the onset of winter.
- Check the coolant every 3 to 6 months to ensure there’s a sufficient amount and that it’s free of rust or other debris.
- Flush the coolant system every 30,000 miles or 2 years to avoid dirt and grime accumulation in the system.
- Use high-quality, manufacturer-recommended coolants to reduce car breakdowns and improve fuel economy.
Make Your Ride Warm and Cozy with AutoNation Mobile Service
A malfunctioning car heater stems from various issues, like a low coolant level, a broken thermostat, or heater core problems. Regular maintenance is crucial for ensuring you don’t get frozen stiff while driving through the snow.
Noticing the signs of a car heater blowing cold air?
AutoNation Mobile Service will have your cabin feeling warm and comfy in no time!
We’re a mobile auto repair service that offers efficient online bookings and upfront pricing. We also provide a 12-month | 12,000-mile warranty on all repairs.
Contact us to get your car heater up and running.