Heat Only Works When Driving – What To Do?

It seems like a season can’t go by without someone having to deal with a mechanical issue. One of the worst examples of this is when your car’s heater isn’t working in the winter.

When your heater only works while you’re driving your car is a common and confusing version of this.

We’ve learned how to keep your car warm when it’s not moving and how to keep it warm when it’s moving.

Several different problems can cause this issue to occur. This list will help you figure out what the problem is and how to fix it.

  • Low coolant
  • Malfunctioning thermostat
  • Air in the system
  • Faulty heater valve
  • Radiator leak 
  • Blocked heater core

Depending on how cold it is, this issue is uncomfortable, inconvenient, and possibly very dangerous.

It’s important to have a basic understanding of how your car’s heating system works to locate what’s causing this.

You can work your way down the list, but it may not do you much good if you don’t know all the ins and outs of each situation.

There is an in-depth look at each possible problem and how to fix it.


Identifying And Fixing The Problem

There can be a variety of places where the culprit comes from. It’s important to narrow it down to a specific list so that you can work through it. 

The best way to find out what is causing the malfunction is to use this method.

As with any mechanic work, make sure you have the right tools and equipment. Let’s take a close look.

Low Coolant

At first, you might not think that your car’s heat can be affected. One of the most common causes of the heating malfunction is having issues with your coolant.

It’s possible to take some of the hot coolants and put them in the heating core of your car’s heater.

The hot air created by the heating core is blown into the car by a fan. It is possible that there isn’t enough of it to divert into the heating core which can cause issues like this one.

If this is the cause of your headaches, you can do several things inside and outside of your car.

If you hear strange noises in your car or notice that your engine is running hotter than normal, it’s probably a coolant issue.

The level of the car’s coolant can be checked. It should not empty quickly. If it’s been a long time since you checked, it might be low. Either that is a leak or not.

The simplest version of this situation is that you have a low coolant. You have to top it off in that case.

If you don’t have a lot of coolants, then you may leak. There is more information on how to diagnose and fix this issue.

Malfunctioning Thermostat

One of the most common causes of this issue is the malfunctioning thermostat inside the system. It’s the thermostat’s job to keep the water out of the radiator.

If it’s stuck open, it’s not doing its job right. This malfunction causes issues with the heater, which is highlighted in the article.

If you have a stuck open thermostat, you will need to replace it. Your car needs to be completely cool first. The thermostat needs to be found at the base of the radiator.

Put a bucket under the hose and remove it. The new thermostat can be used to replace the broken one. If you have to top off your coolant, put the hose on again.

Ensuring that there isn’t air in the system is the most important part of this job. Major issues can come about from that.

How To Check If The Thermostat Is Working?

Start your car and let it run for 10 minutes or so to find out if it’s the problem. Next, shut it off and make sure the hoses are in the correct position.

There should be two hoses, one hot and one cold. If the hoses are hot, then your thermostat is stuck open.

Air In The System

It is a good chance that the heating system is air locked if your car is low on coolant. Air may get into the system when the coolant is low.

When the car is moving, having your heater only work is an indicator of this issue.

A test kit that tells you if there is air in the system can be purchased. A bad cap is one of the most common causes of this issue.

You have to do two things to fix this issue. You need to fix the issue that caused it and then bleed the air out.

A leak in the system is one of the issues that can be the underlying problem.

Faulty Heater Valve

There is a possibility that the issue is due to a malfunctioning heater valve.

The thermostat works the same way as the heater valve but allows the cooling of the heating core instead of the radiators.

Allow your car to run for 10 minutes with the heat on to see if you have an issue. Find the valve that controls the heaters.

Behind the engine is where it is usually found. The valves have hoses on either side of them.

If the engine side hose is hot and the heater side hose is cold, the valve for the engine side hose is faulty.

If it’s cable, vacuum, or electronically operated, you need to figure it out to fix your valve.

Testing the heating valve will allow you to figure out which way it is operated. To fix the issue, you should be able to adjust it manually or electronically.

Radiator Leak

Many of the issues above can be caused by a leak in some part of your boiler. If there is a leak in your car, then it is losing its cooling system.

As we’ve seen, that can cause issues like air blocking and other negative side effects associated with low coolant.

It shouldn’t be hard to find the leak if you just look. Where the hoses connect is a good place to look for coolant leaking around the radiator.

Depending on where the leak is coming from, it can be fixed. It’s a good idea to get a mechanic or a replacement if there’s a crack or other source of damage to your car.

If it’s coming from the end of the hose, that’s a simple fix. The issue should be fixed by holding the hose on tightly.

Blocked Heater Core

Since it’s so small, the heater core can have some issues, which is why it’s usually tucked behind the dashboard.

It can become blocked easily because of the small holes inside. The causes of blockages are usually old coolant and small debris.


How To Test A Heater Core?

Let your car run for around ten minutes with the heat on to see if this is an issue. Then look at the hoses.

The hoses are near the engine. If they are not equally warm, you have some degree of obstruction.

How To Unclog a Heater Core?

A flush agent is the simplest way to fix a heater core obstruction.

These cleaners are specially made to enter your cooling system and clear any obstructions. The core of your heater is included in this.

What Is the Cost to Replace a Heater Core?

It can cost you a lot of money to have your heater core replaced. The lion’s share of the price is due to labor costs.

It is cheap to replace a heating core. A lot of the work is just getting to the location of the heater core which is behind the dashboard.

Is There a Fuse For The Heater In My Car?

There is a problem with your car’s electrical system. It is not likely that the issue of the heater only working while your car is running is caused by a fuse issue.

This is because it controls electricity going to your heating unit. If the fuse blows you wouldn’t be able to use your heater. It’s not just when you are not moving.



It can be difficult to figure out the cause of your car’s problems.

Since your heating issue can be caused by many different things, it’s important to know what they are and how to find them.

It’s possible to go down the list based on how your car is performing and the things you notice about it.

Make sure to be careful and stay safe if the malfunction is the determining issue.

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