Vaillant boiler fault codes

Vaillant Boiler Fault Codes: How to Fix Errors

Last updated on June 9th, 2024

Vaillant boiler fault codes are codes used by Vaillant to show you what the problem might be with your boiler when it has broken down or is not working correctly.

I have been repairing boilers for over a decade and the quicker you fix it the better, so having the boiler error code on the screen when you show up is a great start.

Vaillant Boiler Error Codes

Not all manufacturers use fault codes, but it does help repairers when attending breakdowns as it gives us a good place to start.

Vaillant logo

Sometimes the problem is diagnosed instantly because of the error code. It’s a process of elimination when doing repairs so the fault codes are a big help.

You’ll either find the problem straight away or rule that problem out.

Common Vaillant Errors and Causes

Here are some of the most common Vaillant boiler error codes, with links to posts that go into more detail:

  • F22 Vaillant Fault: Low water pressure – Commonly caused by a leak or from someone bleeding air out of radiators. You might just need to repressurise the boiler
  • F75 Vaillant Fault: Pressure sensor – Commonly caused by dirty water in your central heating system. You might need to clean or replace the pressure sensor
  • F28 Vaillant Fault: No gas – Check if the gas is turned on at the gas meter and make sure there is credit on if it is a prepayment meter
  • F29 Vaillant Fault: No flame detected
  • F27 Vaillant Fault: Incorrect flame detection
  • F83 Vaillant Fault: Temperature sensor
  • F54 Vaillant Fault: Insufficient gas supply
  • F25 Vaillant Fault: Temperature rising too quickly on the flow
  • F73 Vaillant Fault: No pressure change when the pump starts

How to Reset a Vaillant Boiler

The first thing I would check on a Vaillant boiler that is not working, no matter what fault code is showing, is to check the pressure and reset the boiler.

Knowing how to reset a Vaillant boiler is the simplest way to get your boiler working again, as it might have just gone to lockout.

To reset a Vaillant boiler you must find the reset button. This is usually a flame with a line through it.

You have to press the button to reset the boiler. Sometimes you have to hold it down for 3 seconds, but on some Vaillants, it just needs to be pressed.

How to reset a Vaillant boiler
Vaillant ecoTEC plus reset button

Vaillant Pressure Gauge

Vaillant boilers have annoying manual pressure gauges which don’t have any numbers on them, so most people don’t know if it’s on the correct pressure.

It always looks like the pressure is low, even though it’s not. This can lead to raising the pressure too much.

You have to read the digital pressure gauge on the screen to know for sure, but you have to press multiple buttons to find it.

This can be very annoying when working on them as it’s best to leave it turned off until the Vaillant boiler is repressurised.

Vaillant boiler pressure gauge reading
Vaillant pressure gauge reading

Vaillant Boilers Problems

Vaillant boilers, like other boilers, have problems:

  • No heating
  • No hot water
  • Leaking

Some you can learn how to fix yourself, but some will need a registered gas engineer to fix it.

Boiler Not Working No Fault Code

A Vaillant boiler not working with no fault code could be because of:

  • No electricity supply
  • Old Vaillant with no screen which means no fault codes

No Hot Water

If you have a Vaillant boiler with no hot water but the heating is working then this could be for many reasons.

On a combi this is typically:

  • The diverter is stuck or damaged
  • The plate heat exchanger blocked or covered in limescale


A Vaillant boiler leaking can be caused by most parts but in my experience, the plastic diverter valves on Vaillants leak quite regularly.


Vaillant boiler problems can be diagnosed quickly with the use of boiler error codes.

Fixing the problems can sometimes be done without opening the boiler and you should check for some basic things before calling in an engineer.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


How do you clear the fault code on a Vaillant boiler?

You clear the fault code by resetting the boiler. You do this by pressing, and sometimes holding, the reset button.

If the fault code does not clear after resetting, then you will need to find and fix the problem that is causing the error and the boiler to lock out.

Why is my Vaillant boiler flashing?

Your Vaillant boiler is flashing because there is a problem. You will need to read the display and find the boiler error code which will help you to identify the problem.

You should try resetting the boiler before doing anything else as this might get it working again.

What does a flashing radiator symbol mean on a Vaillant boiler?

The flashing radiator symbol means the pump is working to dissipate heat as the boiler has reached the set temperature.

The boiler is not heating anymore but needs to circulate the heat still.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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3 thoughts on “Vaillant Boiler Fault Codes: How to Fix Errors”

  1. Pauline

    I have vailiant boiler and triangle flashing on my thermostat. Showing 0,6 flashing what dies this mean

  2. I have a fault sign of a house with an arrow pointing upwards and a round image at the side of it
    Boiler faults are with small lights – no screens – it’s old but repair guy said it’s the best ever Vaillant boiler – I can’t get hold of him right now!!!!

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