Vaillant F72 Fault Code Meaning, Causes & How to Fix

James Elston
Written by James Elston
Updated on 5th December 2023
Posted on 4th December 2023
vaillant f72 fault code

F72 Vaillant fault code meaning & how to fix it

Vaillant F72 refers to an error code that affects Ecotec Pro and Ecotec Plus models and this fault code indicates that there is an issue in the hot water flow pipe or return pipe thermistors.

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The F72 boiler fault means that the parts may be defective, or the communication between the PCB/ thermistors is not working because of damaged or faulty wiring.

Defective thermistors will need to be replaced, and if they aren’t defective, however, an engineer can resolve the problem without replacing any parts.

If your boiler is 10 years old or more then it may be worth considering whether the cost of a new boiler is a more viable option in the long run, therefore get a fixed price quote online with Boiler Central now.

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What does a Vaillant F72 error message mean?

F72 is the fault code for a problem in the flow or return NTC thermistor. This indicates that the flow and return thermistors are giving inaccurate readings and the difference is too great to cause the Vaillant boilers to lockout

The thermistors monitor the boiler’s water temperature, which is heated by the primary heat exchanger. It should be approximately the same temperature when it returns and leaves.

NTC thermistors change their resistance to temperature. This means that higher temperatures can cause resistance to decrease, while lower temperatures can cause resistance to increase.

The control panel PCB of the boiler converts resistance readings to temperature measurements. The PCB then indicates whether water should or shouldn’t be heated.

If the thermistors do not provide an exact resistance reading, the boiler will not regulate water temperature.

This error means that the boiler mistakenly thinks water entering its system is too hot. This error causes the boiler to not heat water properly and leaves you without heating or hot water.

What causes a Vaillant F72 Error

A boiler that shuts off frequently before central heating or hot taps reach full heat could cause an F72 fault. The advice we like to give here at Boiler Central is that an annual Vaillant boiler service can stop these types of errors from occurring.

Three things can cause the F72 error code in Vaillant boilers.

Broken or Faulty Thermistors

Incorrect resistance readings can be caused by a defective flow NTC thermometer and/or return NTC thermometer.

If the boiler has been used for a while and is starting to get old, these parts may be worn or defective.

This could result in inconsistent and incorrect communication between the PCB and the Vaillant F72 fault code. You should really consider the total costs of getting a boiler repair and consider getting a replacement boiler at the same time as it may be more economical in the long term, as well as lower your energy bills.

Internal Wiring Issue

There may be a problem in the wiring connecting the PCB to one or both of these thermistors. These parts can lead to loosening of connections, even though the wires may have become brittle from vibrations in boilers.

If the thermistors don’t provide the information required, the PCB will not be wired properly or degraded.

This could cause inconsistency among parts.

Installation Error

The Vaillant boiler may have had flow and return thermostats connected to the wrong pipes at the time when you had the Vaillant boiler installed.

It is possible but unlikely. Boilers must be tested before installation. The boiler should be tested during installation. If it had not, the problem would have been immediately detected and the engineer who is qualified to repair the boiler should be contacted.

How to Fix an F72 Vaillant Error

Installation testing will reveal the problem of the thermistors being attached to the wrong pipes and it will be rectified immediately.

If the problem is caused by loose or faulty wiring, an engineer can fix it. It might be necessary to replace wiring that is damaged or faulty.

An engineer will manually measure the temperature in the flow and return pipes to test the thermistors. This will confirm that the temperature readings are accurate or indicate a temperature difference.

The NTC thermistors must be replaced if an engineer discovers that they are giving incorrect readings.

How can you fix a Vaillant F72 error yourself?

You can’t unless you are a fully trained Gas Safe registered heating engineer.

It can be difficult to diagnose electrical problems. It is difficult to diagnose electrical faults without accreditation. This could cause costly mistakes and damage to your boiler.

A registered Gas Safe Engineer should resolve this problem.

What other factors can cause an F72 error?

Sometimes the boiler error code may not be the exact diagnosis. However, it is the closest the boiler can show. These cases might indicate that the thermistors are not the problem.

Another possible cause is limescale buildup. This can cause parts to degrade and incorrect temperature readings.

Limescale buildup can be removed by a professional. A professional will treat the system with a central heating limescale inhibitor, and then fit a scale decreaser to prevent any further limescale buildup. We always suggest here at Boiler Central a magnetic filter and we include them in all our boiler installations.

What do I need to do to reset my Vaillant boiler following an F72 fault?

Once the problem is fixed, the boiler should be reset in order to get it working again. The engineer who repaired the problem will usually do this.

What is the cost of a new thermistor?

Thermistors can be a great choice because they are inexpensive and can easily be replaced for as little as £15 to £40.

The replacement process may take some time and can cost between £160 and£S220.

Is the F72 error a sign that my Vaillant boiler needs to be replaced?

You can request a quote online for a new boiler from all the best Gas Safe engineers. It may be cheaper to replace an older boiler if there are more fault codes. Old boilers also use more energy so energy bills also start to rise. You can get a fixed price quote now online for a new boiler in under 20 seconds with Boiler Central.

Other Vaillant fault code guides

See below our Vaillant fault codes and errors to help you fix your Vaillant boiler problems

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 4th December 2023

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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