The Most Common Vaillant Boiler Faults And How To Fix Them

Valliant boilers are extremely reliable but like any boiler, they can develop faults from time to time. In this guide, we will explain the most common Valliant boiler issues we have come across, detail what is causing the problem, and explain how to fix it.

The first instinct most people have when there is a problem with their boiler is to call out an engineer. Sometimes this is needed, but there are times when you can fix the issue quite simply yourself.

The key is to understand what is causing the problem and that is what this guide is all about. While we can’t explain every possible fault, we can go into more detail about the most common faults.

Our focus in this guide is Valliant boilers. They are generally pretty reliable but there are some faults that we see occurring repeatedly.

In this guide, we will tell you everything you need to know and explain the easiest way to fix it.


Explaining fault codes

When a Valliant boiler does go wrong, the display panel will show a fault code. This code is designed to tell the engineer what the issue is to speed up the fix. But it is something you can use to help you solve the problem and save some money on engineer fees too.

#1 – Low or no pressure

The error code we are asked about most frequently on Valliant boilers is F22.

This fault code is most common on the Valliant Ecotec Plus and Ecotec Pro models, and especially the Vaillant Ecotec Pro 28.

The code refers to a problem with either low or no pressure in the boiler. All boilers have a pressure sensor built-in which monitors the pressure of the water inside the boiler. If this sensor detects a drop in pressure, F22 is the code it produces.

Your boiler is likely to go into lockout mode, as changes in pressure can be dangerous and cause damage to the boiler’s components or even lead to an explosion.

How to Fix it:

The usual recommended fix for an F22 fault is to use the boiler’s filling loop to repressurise the boiler.

This will certainly get the boiler working again, but it is unlikely to fix the issue permanently and you can expect the low pressure error code to reappear in at least a few days if not a few hours!

The most common cause of low pressure in a boiler is a leak somewhere in your central heating system. Until the leak is fixed, the problem will keep reoccurring.

Check all your radiators, towel rails, pipes, and the boiler itself for evidence of a leak. If you find one, see if you can fix it by tightening joints or connections. Otherwise, you will need to get an engineer out to fix the problem for you.

Another possible problem is an issue with your central heating pump. Older models of Valliant boilers quote often use Wilo pumps and these do have a habit of either seizing up or breaking down over time. Such an issue could well result in an F22 error and you would need to get an engineer to take a look to fix that one.

Before you do reach for the filling loop, we recommend you think about the main cause. This is because topping up your system using the filling loop dilutes the crucial chemicals in your central heating system that keep it all functioning properly.

Dilute these too much and you can end up causing more serious problems to the boiler that you already have.

#2 Pump problems

One of the most common problems that can occur with all boilers, and Vaillant models are no different, is with the central heating pump.

This vital component pushes hot water around your central heating system and therefore if it does develop a problem, it is likely that your heating will stop working.

Central heating pump issues most commonly result in error code F75 and is something we see most on theVaillant Eco Tec Plus range and on the Eco Tec Pro 28 in particular.

It generally means there are three possible issues

  1. The central heating pump is faulty – this is the most common cause
  2. The pressure sensor is faulty
  3. Both the pump and the pressure sensor are faulty

How to Fix it:

If you are getting an F75 error code, it is almost certain you have an older model of Vaillant boiler. These older models were fitted with a Wilo pump, as we mentioned above, and these are known for being unreliable and easy to break.

Newer models of Vaillant boilers come with a Grundfos pump which is much more reliable and long-lasting.

To check to see if your pump is the problem, try switching on your hot water or activating your heating. The pump should start to make a gentle humming sound as it begins to work. If you can’t hear this, the pump is probably not working.

This could be caused by various things. A very common issue with Wilo pumps is seized beatings. This is particularly common if your boiler has been switched off for an extended period of time. If this is the issue, the chances are that you will need to get a new pump installed.

Another common problem is that a build-up of sludge and debris in your central heating system can block up the pressure sensor or other components inside the pump. This is also likely to require a replacement although some engineers may attempt to clean it out and see if any permanent damage has been caused.

Other possible pump issues include split or deteriorating seals and possible limescale build-up too (particularly in hard water areas).

Getting a new pump installed is likely to set you back around £300 while a new pressure sensor will cost around £250. If you already have an old boiler, you should give serious consideration to whether it is worth spending this money on replacement parts or whether you would be better off investing in a whole new boiler.

#3 Flame problems

Another common issue with Valliant boilers, and indeed many other boilers too, is with the flame.

This will usually manifest itself in a Valliant boiler as an F27 code on your display panel. There are a number of possible causes for this error code:

  1. The gas valve is not functioning correctly, and as a result, the boiler is not getting the right amount of gas to produce the correct flame.
  2. The flame sensor has an issue.
  3. The ignition leads are faulty and need fixing or replacing.
  4. The printed circuit board (PCB) inside your boiler has a problem and the flame itself is fine.

How to Fix it:

This issue is a more complex one since the number of possible causes is much higher and it could be a problem with the gas supply element of your boiler. As a result, this is one that you will need to get a qualified gas engineer out to take a look at.

If the problem relates to any of the first three possible causes listed above, the good news is that it should be relatively simple to fix. These are small issues and even if you do need to replace the relevant component, this isn’t a big job and the parts are not that expensive.

However, if the issue stems from a problem with the PCB, this is another matter entirely.

The PCB is your boiler’s motherboard – the essential component that links everything else together and keeps the boiler working.

Replacing a PCB is a complex and expensive job and likely to set you back easily in excess of £500.

If this is the cause of your problem and your boiler is already old and out of warranty, it is well worth considering whether you would be better of buying a whole new, energy-efficient boiler.

There are lots of places you can look to buy one of these, but if you visit an online installation site such as WarmZilla, you can get a top-of-the-range model for around £1,700. This makes more sense than spending £500+ on one part when it could easily be another component that goes wrong and costs you more money next week.

#4 Gas supply problems

The next most common Valliant boiler issue we come across relates to issues with the gas supply. This will usually result in either an F22 or F27 code showing up on your display panel.

If there is an issue with the gas supply, your boiler will immediately go into lockout. Gas is extremely dangerous and the built-in failsafe’s in all Valliant boilers will be quick to ensure that there is no risk of further damage.

How to Fix it:

Unless you are a qualified gas engineer yourself, this is not a problem to take on on a DIY basis. You will need a Gas Safe Engineer to sort this one out.

The only thing you should do yourself is to check to see if any other gas-powered appliances in your home, such as your hob, still have a gas supply. If they don’t, this might be an issue with your mains gas supply and you will need to get in touch with your utility company to resolve it.

If this isn’t the issue, you will need to get a gas engineer out and should not mess around with anything.

The engineer will check a number of different things including:

  1. The operation and settings of the gas valve;
  2. The condition of the ignition leads;
  3. The functionality of the ignition unit
  4. Whether the air inlet duct is clear.

Some of these could involve a simple fix or a bit of maintenance, but others can be more serious problems.

If you are quoted a bill in excess of £500 and your boiler is an older model, we would once again suggest that you consider investing in a brand-new energy-efficient boiler.

Where to buy a new boiler

If you are quoted a big price to fix what is already an old boiler, it is generally worth giving some serious thought to investing in a whole new boiler.

These can often only cost a bit more than your replacement parts and come with long warranties are well as being more energy-efficient and so reducing your gas bills too.

If you are going to invest in a new boiler, it is advisable to get several quotes and we would strongly recommend you get one of these from WarmZilla.

WarmZilla is the UK leading online installation company. They offer a wide range of high-quality boilers from all the leading manufacturers and as well as offering the lowest prices around, also have some great special deals too.

Visit their website today and fill in their online form for a fixed-quote with no obligation on your part and no need to enter any personal information. You will be surprised how cheap a high-quality replacement boiler can be with WarmZilla.


If you have a problem with your Vaillant boiler, the chances are that one of the four issues we have detailed in this guide are to blame.

We have explained what causes each problem and outlined the fixes you will need to do.

In some cases, where a major component needs replacing, you might want to consider buying a new boiler and we have recommended you get a quote from WarmZilla to do so.

Have you had problems with your Vaillant boiler? Do you have any questions we haven’t addressed in this guide? Any tips for our readers we haven’t touched on?

It is always useful for readers to hear about the experiences of others in addition to our expert advice, so why not share your thoughts now using the comment box below?

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