Vaillant f72 fault code

Vaillant F72 is an error code that affects Ecotec Pro, Ecotec Plus, and Ecotec Exclusive models. This means there is an issue with the flow or return thermistors.

Either the parts are defective or the communication between the thermistors/PCB is not working due to damaged or faulty wiring.

Thermistors that are defective will need to be replaced. However, if they are not defective, an engineer should resolve the issue without replacing any of the parts.

What Does a Vaillant F72 error code mean?

F72 is the fault code that indicates a problem with the flow or/or return NTC thermistor. This means that the thermistors have been giving incorrect readings, and the difference between them is too large to cause the boilers shut off or lock out

The boiler’s water temperature that is heated up by the primary heat exchanger is monitored by the thermistors and should be around the same temperature when it leaves and returns.

NTC thermistors alter their resistance to temperature. This means that higher temperatures will cause the resistance to decrease and lower temperatures will cause the resistance increase.

The boiler’s control panel PCB converts resistance readings into temperature measurements. It then signals whether water should be heated or not.

The boiler will not regulate the water’s temperature if the thermistors don’t provide an accurate resistance reading.

This error basically means that the boiler is mistaking water entering its system for too hot, when it has not. This error causes the boiler not to heat water as it should, and you are left without hot or heating water.

What Causes a Vaillant F72 Error

An F72 error in your boiler could be a boiler that shuts off repeatedly before central heating or hot taps reach full heat, hot water that is too hot or the boiler shutting off repeatedly.

The F72 error code can be caused by three things.

Faulty Thermistors

Faulty flow NTC thermistor and/or return NTC thermistor are causing incorrect resistance readings.

These parts could be defective or worn out if the boiler has been in use for some time.

This would result in inconsistent and incorrect communication with the PCB, which triggers the Vaillant F72 code.

Wiring Issue

It is possible that there is a problem with the wiring between the PCB and one or both of the thermistors. Although the wires might have become brittle over time due to vibrations in boilers, these parts can cause loosening connections.

A PCB that isn’t receiving the required information from the thermistors will be degraded or without proper wiring.

This could lead to inconsistency between parts.

Installation Error

When you had the Vaillant boiler installed it may have had the flow and return thermistors connected to the wrong pipes when the installation took place.

This is possible, but it is unlikely. Boilers are tested during installation. If the boiler had shut down, this error would have been detected immediately and you should get the recommended competent heating engineer back to fix the issue.

How to Fix an F72 Vaillant Error

The problem with the thermistors being connected to the wrong pipes will be detected during installation testing and rectified immediately.

An engineer can tighten the connections and fix the problem if loose wiring or connections are the cause. If the wiring is faulty or degraded, it might need to be replaced.

To test the thermistors, an engineer will manually measure temperature in the return and flow pipes. This will verify that the readings are correct or if there is a temperature difference.

If an engineer finds that the thermistors provide incorrect readings, the thermistors will need to be replaced.

How can you fix a Vaillant F72 error yourself?


It is difficult to diagnose electrical faults. Attempting to fix such an issue without proper accreditation could lead to a costly misdiagnosis, as well as damage to your Vaillant boiler.

This problem should be resolved by a registered Gas Safe Engineer.

What else can cause an F72 error to show?

Sometimes, the boiler error code is not the exact diagnosis, but it’s the closest the boiler can show. In these cases, the thermistors might not be the problem.

Limescale buildup is another possible cause. This can lead to parts degrading and inaccurate temperature readings.

A professional can help you get rid of limescale buildup. They will douse the system with a limescale inhibitor and fit a scale reducer that will prevent further buildup.

Do I need to reset my Vaillant boiler after an F72 fault?

After the problem has been fixed, the boiler must be reset to start working again. This will be usually done by the engineer who fixed the problem.

How much is a new thermistor?

Thermistors are a great option because they are relatively inexpensive and can be replaced for as low as £20 to £40.

The replacement process can take a while and will cost between £160-£220.

Does the F72 error mean I need a new boiler?

All the top Gas Safe engineers are available to help you and you can get a fixed price quote on a new boiler online now. If you have an old boiler then potentially it may be more economical to replace your boiler as more fault codes could start to appear and old boilers are much less energy efficient.

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