Why does my car heater only work when am driving?

On a cold day, you come to a halt in your car, and the heat in your cabin abruptly turns into an icy blast. What’s going on? Learn what’s causing your car heater to only function when you’re driving and what you can do about it this season to stay warm.

This issue can be caused by a variety of factors. This list given below will assist you in troubleshooting the problem and learning how to potentially resolve it. This is an unpleasant, difficult, and sometimes dangerous situation, depending on how cold it is outside. To figure out what’s causing this, you’ll need a basic understanding of how your car’s heating system works, and you’ll know the reasons why your car heater core only works when you’re driving.

Car heater core only work when am driving

You can work your way down the list, but you won’t get very far unless you understand every detail of each circumstance. Continue reading to discover more about each potential issue and how to resolve it.

Read more: How to pressure test an engine cooling system and why

Why does your car heater work only when driving?

The heater in your car works hand in hand with the cooling system in your engine. Many problems with cabin heat inconsistency can be traced back to coolant concerns. The following factors may be a hindrance if your automobile only provides heat when you’re driving.

  • Low Coolant
  • Faulty Thermostat
  • Air in the System
  • Bad Heater Valve
  • Radiator Leak
  • Blocked Heater Core


Low Coolant

The temperature of the engine and the flow of hot air into the cabin are both controlled by coolant. When your engine is running, it generates a lot of heat, which coolant helps to collect by transferring it to your vehicle’s radiator for cooling. If the coolant in your car is low and the heater is turned on, you may discover that the heating only works when you’re driving.

Many components in your car rely on a properly functioning cooling system, and no heat at idle is usually a clue that something is wrong. In this case, the first thing you should do is check your coolant level.

Never open a cooling system that appears to be hot or pressured. This could result in personal injury. Check your owner’s manual for instructions on how to check coolant levels, or hire a professional to do so for you. Low coolant levels can be caused by a variety of factors, including poor maintenance and leaks in the cooling system.

Read more: Understanding the working of a heater core

Faulty Thermostat

Another common reason for this problem is a faulty thermostat inside your system that remains open. The thermostat’s job is to ensure that coolant is filtered into the radiator.

It’s not doing its job effectively if it’s jammed open. This malfunction leads to problems with the heater, such as the one described in this article. You’ll have to replace your jammed open thermostat to get it fixed. To begin, ensure that your vehicle is fully cool. Next, look for the thermostat near the radiator’s base.

Remove the radiator hose by placing it in a bucket and then removing it. You can now install a new thermostat in place of the broken one. Replace the pipe and, if necessary, fill off your coolant. The most crucial aspect of this work is to ensure that there is no air in the system. This could lead to severe problems in the future.

How Can You Tell If Your Car’s Thermostat Is Working? Start your car and let it run for around 10 minutes to see whether this is the problem. Then turn it off and inspect the radiator hoses carefully. One hose should be hot and the other should be chilly. Your thermostat is stuck open if both houses are hot.

Air in the System

If your car’s coolant level is low, it’s likely that the heating system is air-locked. When the coolant level is low for whatever reason, air enters the system.

The fact that your heater only works when the car is moving is a clear sign of this problem. A coolant system test kit can be purchased to determine whether or not there is air in the system. A faulty radiator cap is a common cause of this problem.

There are two steps to resolving this problem. You must solve the underlying problem that produced it, as well as bleed the air out. A damaged radiator cap, low coolant, a leak in the system, and other factors could be to blame.

Bad Heater Valve

A faulty heater valve is the next likely cause of the problem. The heater valve functions in the same way as a thermostat, but it permits coolant to flow into the heating core rather than the radiator. Allow your car to run for around 10 minutes with the heat on to diagnose the problem.

After that, look for the heater valve. It’s usually found behind the engine, on the firewall. Touch the hoses on either side of the valve with care. The heater valve is malfunctioning if the engine side hose is hot and the heater side hose is cool.

To repair your heater valve, you must first determine whether it is operated by cable, vacuum, or electrically. You can test the heating valve that corresponds to the operating manner by determining which way it is operated. To remedy the problem, you should be able to adjust it manually, with a vacuum, or electrically.

Radiator Leak

Many of the troubles listed above can be caused by a leak in some component of your radiator. Your car is losing coolant if there is a leak someplace. As we’ve seen, this can result in heater troubles such as air obstruction and other severe consequences of low coolant.

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By simply looking, you should be able to locate the leak quite quickly. Check for coolant leaks near the radiator, particularly where the hoses attach.

The solution to this problem is contingent on the source of the leak. If your radiator has a crack or other source of damage, it will almost certainly need to be repaired or replaced. If the leak is coming from the hose’s end, though, it’s a straightforward remedy. Simply tighten the clamp that holds the hose in place, and the problem should be resolved.

Blocked Heater Core

Because of its small size, the heater core is usually hidden under your dashboard and might cause problems. It’s easy for the little openings within to become clogged. Old coolant, as well as dirt and other tiny debris, are the most common causes of blockages.

What Is the Best Way to Test a Heater Core? Allow your car to idle for 10 minutes with the heat on to check whether this is the problem. After that, double-check the hoses. The heater core hoses are located behind the engine on the firewall. If they aren’t both heated, you’re most likely dealing with a blockage.

What Is the Best Way to Unclog a Heater Core? A flushing agent is the simplest technique to clear a heater core obstruction. These cleansers are precisely designed to penetrate your cooling system securely and clear any clogs. This includes the core of your heater.

Read more: How can I replace a bad thermostat in my car?


During winter, car heaters are of good use since they use the engine heat to serve another purpose in the car interior. As a car owner, you need to know when your car heater is faulty and the common causes of these problems. In this article, we’ve listed some common causes why your car heater only works when you’re driving.

I hope you learn a lot from the reading, if so, kindly share with others. Thanks for reading, see you around!