You switch on the heater and crank it up, expecting a wave of warm air.
Instead, you get hit with an icy blast and maybe even a musty smell.
A broken thermostat or a clogged heater core could be why your car heater isn’t working.
But, how do you know what’s causing the issue?
To help you figure it out, we’ll explore the causes of a faulty heater and go over the steps to fix it once and for all.
Let’s begin!
This Article Contains:
- 9 Common Reasons for a Car Heater Not Working
- What Other Symptoms Indicate Your Car Heater Is Failing?
- How to Diagnose and Fix a Broken Car Heater
- How Much Does a Car Heater Repair Cost?
- 3 FAQs on Car Heaters
9 Common Reasons for a Car Heater Not Working
A car heater can malfunction due to:
1. Low Coolant Level or Contaminated Fluid
Usually, your car’s heater core transfers the heat from the coolant (antifreeze) to the air to warm the cabin.
However, a cracked radiator hose or a broken water pump can cause an engine coolant leak, reducing the quantity. If there’s insufficient coolant to absorb the engine heat, your car’s vents will blow cold air.
Contaminated coolant can also cause trouble, as regular heating system use can allow dirt and grime to enter the system and degrade the fluid. This impure coolant damages the water pump and radiator, preventing your heating system from functioning correctly.
2. 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, it can get stuck open or closed. When the thermostat is stuck closed, heated coolant cannot reach the heater core, stopping the system from blowing hot air.
3. Clogged Heater Core
The heater core transfers heat from the engine coolant to warm the air. Then, the heater fan pushes the hot air into the cabin.
However, the heater core’s tubing can get clogged with old, contaminated antifreeze or debris. The hot coolant can’t flow through the tubes to heat the air when this accumulation increases.
4. Broken Heating Controls
To activate a car’s heater, you have to adjust the climate control knob or dial, which sends signals to the HVAC parts to begin circulating warm air. But if the control’s wiring is loose or damaged, the system won’t work properly, and your cabin will stay cold.
5. Failing Heater Control Valve
Another possible issue is a malfunctioning heater control valve. This valve regulates how much hot coolant flows into the heater core. If the heater control valve isn’t working efficiently, there may not be enough coolant to heat the air that blows into the cabin.
6. 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 core, which makes it hard for warm air to reach the cabin.
7. Blower Motor Problems
The blower motor circulates air within the HVAC (heating, ventilation, and air conditioning) system to ensure proper ventilation.
However, the airflow may be inconsistent if the blower motor resistor that controls the fan speed is damaged. So, even if the heater works, a malfunctioning blower motor will prevent warm air from reaching the cabin.
8. Radiator Troubles
The radiator usually cools the heated 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.
NOTE: A cracked water pump or stuck blend door can also stop engine coolant from reaching the heater core, causing cold air to blow from the vents.
9. Electrical Issues
Wires and fuses can corrode, becoming damaged over time from age or moisture in the system. This electrical issue prevents heating components from receiving enough power to operate correctly.
Now that you know why your heater is blowing cold air, let’s check out the key signs of a bad heater.
What Other Symptoms Indicate Your Car Heater Is Failing?
Lack of heat is the most obvious sign of a malfunctioning heating system. This problem usually happens when the damaged heater core or blower fan affects the heating process.
Additional symptoms include:
- An odd, musty odor in the cabin: A coolant leak or moisture accumulation in the heating and air conditioning system can produce a strange, musty smell. Both need urgent attention, as a leaky radiator causes engine overheating, and moisture can promote unhealthy mold growth.
- Abnormal noises from the HVAC system: If you hear rattling, squealing, or hissing when you turn on the heater, it could signal a faulty blower motor. The sounds may also occur due to broken parts within the heater core or air in the cooling system.
- A foggy windshield: To defog a windshield, you need a working defroster. However, the defroster won’t work if there’s insufficient or improper coolant flow.
- Steam emitting from the engine: Smoke under the hood indicates engine overheating due to a coolant leak. A damaged radiator or cracked HVAC hoses can cause this leak.
Spotted some of these warning signs?
Keep reading to see how to repair the heater and stop these symptoms for good.
How to Diagnose and Fix a Broken Car Heater
Determining and repairing the faulty part of your car’s heating system requires accessing multiple components in the engine bay. You’ll also need technical experience and knowledge to perform the task. If you find it overwhelming, it’s better to let an expert handle it.
Here’s what a mechanic would do:
1. Inspect the Coolant Level and Quality
The mechanic will check the coolant reservoir for leaks and ensure the fluid 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.
Fix: If there’s insufficient coolant, the technician will top up to the recommended level. In case the fluid is contaminated, they’ll flush the cooling system and add a new batch.
2. Check the Engine Temperature
They’ll use an infrared thermometer to verify if the engine temperature is within the normal range of 195°F and 220°F (90°C – 105°C). If it’s outside the normal operating temperature, there’s likely a faulty thermostat.
Fix: They’ll open the car’s hood to access the thermostat at the base of the radiator (between the heater core and the main hose). Then, they’ll detach the radiator hose at the base to drain the coolant system. Afterward, they’ll remove the faulty thermostat and install a new one.
3. Inspect the Heater Core
Next, they’ll open the heater box, check the hoses, and look for signs of a faulty heater core.
Fix: If the heater hoses are clogged, they’ll attach a garden hose to run clean water through them. But if the heater core issue persists, they’ll locate and change the faulty component.
4. Assess the Cabin Air Filter
Cabin filters can accumulate dirt and debris over time, requiring routine checks. A mechanic will detach the glovebox to access the cabin filter and inspect it.
Fix: If your car has a reusable filter and it’s dirty, they’ll submerge it in a bucket filled with a mild detergent solution and wipe it gently with a towel. However, if it’s made of non-reusable material, like paper, or its pleats are damaged, they’ll install a new cabin filter.
5. Test the Blower Motor
They’ll look for loose electrical connections around the motor and use a multimeter to check for electrical continuity or identify a blown fuse. They’ll also turn on the heater to listen for unusual noises, often from a failing motor or debris caught in the blower fan.
Fix: Based on the inspection, they’ll restore the electrical connections, change the fuse, or replace the blower motor and fan.
6. Check the Heater Controls, Valve, and Electrical Connections
The mechanic will test the heater controls, valves, knobs, and wiring to see if they’re stuck, non-responsive, or damaged.
Fix: If controls are broken, they’ll replace them. In case of loose or cracked wires, they’ll swap them out for new ones.
7. Examine the Radiator
They’ll check the radiator for signs of blockages, cracks, or internal corrosion that might affect coolant circulation to the heater core.
Fix: If the radiator is clogged, they’ll flush it. But if it’s cracked or leaking, they’ll replace it.
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 the average cost estimates (including parts and labor):
- Coolant flush: $140 to $250
- Thermostat replacement: $200 to $750
- Blower motor replacement: $360 to $420
- Wiring harness replacement: $1,050 to $1,550
- Radiator replacement: $1,100 to $1,260
- Heater core replacement: $1,300 to $1,830
Are you curious to know more about your car’s heating system?
Check out the common queries car owners have.
3 FAQs on Car Heaters
Here are answers to some questions on heaters that you should know:
1. How Does a Car Heater Work?
Most cars with a heating system use hot coolant to warm 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. The coolant flows through the core’s fins, where the heater 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 enters the cabin through the HVAC ducts and vents.
2. Do Heater Problems Need Urgent Attention?
Yes, you should take your car to a mechanic if the heater doesn’t work.
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, you’ll have reduced visibility, a safety hazard.
Moreover, if you don’t fix issues like a coolant leak or a faulty blower motor, they can cause overheating. This excess heat can damage various parts, such as the heater core or radiator, resulting in high engine repair costs.
3. How to Prevent a Car Heater Problem
To avoid a car heater issue:
- Schedule regular car maintenance of the thermostat, blower fan, and other heating system parts once a year before the onset of winter.
- Check the coolant every three to six 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 two years to avoid dirt and grime accumulation.
- 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 car maintenance ensures you don’t get frozen stiff while driving through the snow.
Already freezing in your seat despite cranking up the heater?
It’s time to call AutoNation Mobile Service.
Our experts will make your cabin feel warm and comfy in no time!
We offer easy online bookings, upfront pricing, and a 12-month, 12,000-mile repair warranty so you can relax even if unexpected problems arise.
Reach out today to get your car heater up and running.