How to Fix a Cargo Van that Won’t Heat Up

If your cargo van won’t heat up, this is how to fix it:

  1. Top up Coolant level if its too low
  2. Flush coolant system to remove air bubbles
  3. Flush heating core with a flush tee kit
  4. Replace thermostat if it’s stuck
  5. Replace Faulty Cooling Fan switch
  6. Change Heater Control Valve – If Closed, disconnected or leaking
  7. Blend Door – Stuck in closed position

It is important that when you notice your van not heating up,you resolve itas soon as possible. This is because if the heater is not working, during cold weather it may not only be uncomfortable but could also be dangerous.

When the van’s heater is not working as it should, the windshield could quickly fog up, making it almost impossible to see. Hopefully you will therefore notice the problem prior to the days getting any colder.

While there are some problems with the heating system which you cannot probably fix on your own, fortunately many of them you can.

To determine why the van will not heat and therefore hopefully fix the problem, we must first understand how the heating system works.

Many people make the assumption that coolant is only required to keep the engine from overheating. While the coolant’s primary objective may be that, it is also an intricate part of the heating system.

As coolant passes around the engine, it absorbs heat some of which, when required, is transferred to the heating core which provides heat to the rest of the van. A fan then blows the warm air around the heating core to where you direct it using the vents and control panel in the van.

This means that a heating problem could be caused by the quantity and condition of the coolant, one of the valves or doors, the fan or controls.

You can easily check thequantity of coolant,,but can also further determine the problem by checking the heat of certain hoses in the system. This should direct you to the actual cause of the problem so you can decide to fix it on your own or seek professional assistance.


Fill Up Coolant Level if It Is Low

Coolant is an intricate part of your van. The coolant is pushed through the radiator and heating core where an exchange of temperature occurs. If the coolant level is low, not only will this expose the engine to overheating but will also impair the efficiency of the internal heating system.

A low coolant level is probably the most common culprit for a van’s heater not to work. Fortunately this is something you can remedy without much cost.

Your radiator needs to be full and the coolant reservoir full to the max marking. While they should be full care should be taken not to overfill it.

The coolant may be reducing due to a leak, so you can check this. With the radiator and coolant levels full, leave the radiator cap off, start the engine and turn the heater on full. If the coolant level drops then you will have a leak.

If you do not find and repair the leak you will always be having problems with your heater but worse, your engine may start to overheat.


Remove Air Bubbles From The Coolant

If there are any air pockets in the coolant, it will impede the efficiency of the coolant to transfer heat to the heating core.

To resolve this problem, you will need to take the same actions as if you have a lack of coolant.

This time however, when you top up the coolant with the engine on and the heater on full, it should quickly fill. Do not forget though, to keep the radiator cap off though so any air pockets can free themselves.

This should not need doing often but if it does, you will once again want to check for any leaks in the system.


Flush Clogged Heating Core With a Flush Tee Kit

The heating core removes heat from the coolant, and a fan then blows over the core, carrying warm air to the heater and windshield.

If the core is blocked it will not be able to draw heat from the coolant and so its surrounding air will remain cool.

The heating core is located behind the van’s glove box and is connected to two hoses. If both the hoses feel warm, the core is probably good, but if only one is warm, the core is blocked.

Changing the heating core is a job for a professional. However, flushing the heat core will usually solve the problem and clear the blockage. To flush the system yourself you will need to buy a ‘flush tee kit’.

Having got your flush tee kit, you can follow the instructions here in order to flush the heating core.


Replace the Thermostat if It Is Stuck

The thermostat is a relatively simple but critical device. When the engine is cold, the thermostat prevents coolant from reaching the engine otherwise the engine would take too long to warm up and start.

When the engine has warmed up, it allows coolant to run through and stop the engine from overheating.

If the thermostat is stuck in the shut position, it will not allow coolant to reach the engine, and thereby the engine will overheat.

If however the thermostat is stuck in the open position, coolant will uninterruptedly flow through the engine, failing to allow it to heat up.

If the thermostat is stuck in open, the coolant will not get hot and therefore cannot transfer heat to the heating core. This will result in the heater not giving out heat.

Although a stuck thermostat will usually need replacing, it is a task which most people can do without professional help.


Replace Faulty Cooling Fan Switch

If the switch for the cooling fan is stuck, it can have the same consequences as a stuck thermostat and therefore inhibit the air from heating up.

Over time and continued use, some of the buttons on the heating control can become stuck or broken.

Although you may be able to replace a broken button on your own, due to complexity of the system usually professional help is needed to ascertain the exact problem.


Change the Heater Control Valve if It’s Stuck

Unlike the thermostat, which opens and closes automatically depending on temperature, the temperature control valve will only work when positioned to.

The control valve determines if coolant is sent to the heater core or not. If this valve is stuck in the closed position, then no coolant will reach the heating core, and no heat will be available for the inside of the van.

Like with the heater core, you can check if the hoses to and from the control valve are both warm. If the hose from the control valve to the heating core is cool, then the control valve is closed.

While you can change the heating valve on your own, if that does not fix the problem you will need a mechanic to perform full diagnostic checks.


Blend Door

Not to be confused with the mode door which controls the mix of heat to the floor and windshield, the blend door controls the mix of cold and hot air inside the van.

If the blend door is stuck or faulty, you will have no control over the heating system.

Unfortunately if you determine that the blend door is the problem, perhaps only allowing cold air in, this is a job for a professional mechanic to solve.



As you can see there are many different aspects which can cause your van not to heat when you want it to. Fortunately though, many of them you can address on your own and at a minimal cost.

To try and avoid any of these problems though, you should have your heating system checked periodically. Even if you do not have the full system checked, you should at the very least change your coolant every couple of years or every 30,000 miles.

As with most things on the van, one problem may just be the start of a much larger and more expensive problem accumulating. So as well as for comfort and safety, you will want to solve the problem before it potentially becomes more costly to do so.

If you do not usually use the van’s heater during the warmer months, it may be worth checking it at least once prior to the colder weather commencing. This will give you time to fix any problems before you experience discomfort and perhaps put your safety and finances at risk more than necessary.