Fixing Car Heater That Only Works When Accelerating – Complete Guide

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Car heaters are essential when it is winter and snowfalls everywhere. Car owners will require heaters to keep them warm so that they don’t freeze and die. While using the car heater, sometimes it can suddenly blow out in the middle of the winter season, leaving you depressed about how your car heater avoids freezing.

Several reasons can make your car heater blow out. For instance, your car water leaks, damaged heat controls, damaged heater core, thermostat not functioning, and less enough cooling system in the engine. When you experience such a problem, you can use the steps to help you fix your car heater.

Table of Contents

Reasons why your car heater is not functioning as required

Many reasons can affect your car heater and make it not function properly. They include:

  1. Heater core clogged
  2. Damaged heater fan
  3. Faulty blower motor resistor
  4. Car water leakages
  5. Faulty HVAC controllers
  6. Damaged thermostat
  7. Low car coolant or antifreeze
  8. Blown car wires or fuses

Steps by step guide on how to fix car heaters that only work when accelerating

Step 1: Check your car heater control valve

Heater control performs many functions, such as allowing hot water to flow when the power required is higher than when accelerating. First, identify any problems with your car control valve. For example, lower the car back, remove hot air continuously, and hotter air conditioning when you are still accelerating.

The heat control valve must be fixed instantly depending on the type of valve in your car engine. Try removing damaged parts from the car engine. Once removed, fix the spare car heater control valve, which is primarily manual, and tries testing your car heater.

car heater not working

Step 2: Coolant or antifreeze

When accelerating, the coolant level is activated to cool down your car engine, especially when the weather is hot. When it is winter, bring your antifreeze over from the engine to your car’s heater core. Warm air is blown as a result into you when you are accelerating.

Your antifreeze will work when your car engine is not accelerating, and you can feel a lot of colds. Once you turn your car engine on, your antifreeze warms up and starts providing heating to your car. If the antifreeze is not working, first check the coolant level and ensure it is high. If the coolant level falls off, warm air is not created, resulting from freezing temperature.

Step 3: Check car heater core

If you are not accelerating, hot air will not be released from the car engine, and therefore the heater core will not function as required. Once you accelerate your car engine and still the heater core fails to function as required, inspect the heater core and identify any problems affecting the heater core.

If you suspect that your heater core is damaged or not working correctly, consider the signs below

  1. Snow inside your car
  2. Car coolant functions faster
  3. Too much cold inside the car
  4. A sweet-smelling scent
  5. Car engine overheating

Try troubleshooting your heater core problems by getting rid of any dirt that blocks warm air passage by flushing your heater passage. If the flushing method fails to work, try fixing the heater core by following the manufacturer’s instructions.

Step 4: clogged or broken car heater controls

Your heater control may be damaged if you have used it for so long without changing, resulting in them not functioning anymore. Sometimes your heater control can be in good condition but still not function due to damaged heater core buttons.

To fix the problem, ensure you replace your heater control button.

If the heater control button is working correctly, then inspect your heater core and identify any problems. Try fixing the problem that identifies the continuous blowing of warm air into the cabin, warming up your car.

Finally, ensure you follow the manufacturer’s instructions carefully when fixing your car heater control to avoid damaging the heater control further.

Step 6: Check car water leaks

Once your car water starts leaking, the car heater will stop functioning as usual. A powerful and effective heating system can make you have fun during the winter season. If you can’t get your car heat leaving the vents, call any nearby repairing shop to help you fix the water leaks problem. Ignoring the problem results in more extensive damages while accelerating than when contacting a mechanic.

Step 7: The broken thermostat

The thermostat works when you are accelerating, but if you notice that your thermostat indicates “C” even when you are accelerating, you may have damaged your thermostat, and it requires immediate troubleshooting. If your thermostat fails to function correctly, a signal of the car engine is warm and will not be sent to the heater core to provide warmth inside the car. You can fix your thermostat or replace it with a new one.

You can troubleshoot your thermostat by following the steps below.

  1. Once your thermostat stops functioning, stop your car and leave it to sit for 10 to 20 minutes. Leaving the car for these minutes ensures that your car is cooled.
  2. Find the position of your car’s thermostat. In all cars, it is found between the central hose and the core.
  3. Pull the radiator cap gently and lift the front end of the vehicle to see the thermostat.
  4. Dismantle the main hose and remove all the coolant from the radiator.
  5. Slowly remove the thermostat and try fixing it if fixable. If not fixable, replace the thermostat with a new one that suits your car.
  6. Reinstall the main hose to the car radiator.
  7. Place the coolant in its appropriate position, that is, cap back on the reservoir.
  8. Slowly return your car to its normal position by lowering it.
  9. Turn on your car engine and wait to see if there is any heat released.
  10. Test your thermostat by driving some miles. If thermostat fixation is not successful, try attaching it or contacting a nearby mechanic to help you install the new thermostat.

Frequently asked questions

Does my car heater use fuel?

Your car heater core requires oil to function correctly.


Every car experiences some flaws, such as the heater core working when your car is accelerating and faulty thermostats. In this article, the steps will help you troubleshoot the car heater only working when accelerating. The steps are simple and easy to apply for both professionals and non-professionals.

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