Common Vaillant Boiler Faults and How to Fix Them

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Last updated: October 31, 2023

Founded in Germany in the 1970s, Vaillant boilers have been a dominant feature in home heating systems and central heating for many decades. A popular and reliable choice for many homes, whether they have combi, regular or system boiler model, there are currently 11 boiler ranges in the Vaillant stable, including the popular eEcoFit, EcoTec and EcoTec Plus.

While Vaillant have a reputation for quality and affordability, like all boilers they can also be prone to faults over time. And there are a few glitches that are common issues across the Vaillant range.

As central heating and hot water issues are the last thing you want in your home, especially during the colder months, it makes sense to also know the likely causes if you have a Vaillant boiler system in your home. And a little prior knowledge can not only save you time, as well as help you to avoid cold showers, it can also save you on expensive repair or energy bills.

To help keep your Vaillant boiler happily running, we take a look at common Vaillant boiler problems, what those fault codes mean and how to fix them.

Error codes for common Vaillant boiler issues:

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Low Water Pressure

Low water pressure will affect all boilers at some point in their working life, and your Vaillant boiler should be monitoring the water pressure in case it drops below the normal level, which is typically 1 – 1.5 bar.

Anything below 1 bar is considered under pressured and this issue is a common feature in the Ecotec Plus and Ecotec Pro models, including the Vaillant Ecotec Pro 28. Should your boiler experience low pressure, especially if it is a sudden drop, then it’s a sign there is an issue with your boiler and the F22 fault code will show on its digital display.

  • The possible causes – a water leak is the likely cause of sudden low pressure and can be found anywhere in your system, from the boiler itself to pipework and radiators. A check of your central heating and hot water system could reveal signs of a leak, including damp walls and floors. A build-up of air in your radiators can also cause low pressure as the air causes a blockage which slows down the water flow. Alternatively, it could be a faulty pump or pressure relief valve.
  • The fix – if there is no obvious sign of a leak, then repressurising the system using the boiler’s internal or external filling loop may well rectify the problem and bring the boiler back to normal on the pressure gauge. But if this doesn’t work and the F22 error remains, or you suspect a leak, then you need to call out a Gas Safe registered engineer to correctly diagnose and fix the problem.

Failed Ignition

Boiler ignition failure will leave you without heating or hot water if it is not resolved so this is not an issue to ignore. Your ignition is essential, and it keeps the flame burning, which in turn heats up water as it passes through the pipe. A faulty or failed ignition is a relatively common issue with Vaillant boilers and will be displayed as an F28 fault code which you need to look into.

  • The possible causes – there are several main reasons why your Vaillant Combi boiler’s ignition is refusing to light. The first is an issue with your gas supply, meaning there is no fuel to feed the ignition process. Alternatively, it could be a frozen condensate pipe, which takes vapour and waste water out of the boiler and into an outside drain and can cause a shutdown of your boiler, including the pilot light. The third reason could be faulty electrode or ignition leads which can wear out and means your boiler’s ignition cannot create the essential spark to get things started.
  • The fix – if you suspect an issue with the gas supply, check any other gas appliance in your home to see they are still working. If not, then check your gas meter and call your energy supplier. For a frozen condensate pipe, see further down in this guide. However, if it looks like it is down to faulty electrode or ignition leads, then you need to call out a Gas Safe registered engineer who can get inside your boiler unit to check the condition of the ignition and hopefully rectify the issue. However, it is a problem with the printed circuit board or if your boiler is over 10 years old, it may be time for a newer model.

Faulty Pressure Sensor or Pump

A common fault, particularly in the Vaillant Ecotec boilers, an F75 error code is telling you that the boiler is unable to detect sufficient pressure from the internal pump. If the heating pump is not working as it should then your heating and hot water will be decidedly under par, taking much longer to heat up and even not reaching any decent temperature.

  • The possible causes – while newer models operate with a more effective Grundfos pump, older Vaillant models use a Wilo pump which have higher failure rates and are known to eventually breakdown. The result of a broken pump is that it is unable to push the circulating water as fast as it should around your heating system and to your hot water taps.
  • Dirt and sludge can also build up in the pump, blocking its components and causing them to eventually fail. Alternatively, a faulty pressure sensor could be to blame for that F75 error code.
  • The fix – as the boiler is an internal component, it is advisable to call out a Gas Safe engineer to assess and fix any problems with your pump or pressure sensor. If you have an older model, the pump can be upgraded, and the system flushed to get rid of all that debris build-up. The engineer can also replace a faulty pressure sensor if that is found to be the real cause of the error code display.

Frozen Condensate Pipe

Now to the possibility of the condensate pipe causing a boiler fault with your Vaillant. Your boiler’s condensate pipe is essential for the healthy running of your boiler as it drains condensate waste away, normally to a drain outside. If you have an issue with your condensate pipe, you should see either fault code F27 or F28 showing on your boiler’s display. Ultimately a malfunction with your condensate pipe will cause your boiler to lockout.

  • The possible causes – an obstruction in the condensate pipe will prevent the waste being removed from your boiler, which is a situation you don’t really want. Frozen water inside the condensate pipe is a likely culprit, particularly during very cold winter months and if the pipe is not well insulated. Dirt and debris can also cause a blockage in the pipework.
  • The fix – a frozen condensate pipe is a relatively easy DIY fix – simply pour hot (but not boiling) water over the pipe to melt the frozen water and get the pipe running smoothly again. However, if this doesn’t work, or it is more likely to be a debris blockage you can’t remove, get in touch with a Gas Safe engineer.

Poor Flow Rate From Taps

Your system’s flow rate is simply the rate at which water comes out of your taps or the showerhead. If this rate is slow, then it is considered a poor flow rate and will be seen when you first turn the taps or shower on – the water will take time to come out and will then not increase in flow or pressure.

  • The possible causes – low pressure is the cause of a poor flow rate, as there is not enough pressure in your boiler to push the hot water sufficiently around your heating and hot water system. This drop in water pressure can be caused by a faulty pump or be due to the height and position of the water tanks in your home. Issues with an open-vent heating system – which is seen on older boilers and has a feed and expansion tank – can also be to blame.
  • The fix – low pressure (below 1 bar) in your boiler can be fixed by re-pressurising your boiler so that it comes back to the normal pressure range. Depending on whether you have an internal or external filling loop, always follow your manufacturer’s instructions when repressurising your boiler to reset it to where it should be. If this doesn’t improve your water flow rate, get in touch with an engineer who can diagnose and fix the problem – which could be by replacing the pump or raise the height of the tank in your loft.

Incorrect Flame Detection

Incorrect flame detection – F27 error code on your boiler’s display – means the boiler’s flame sensor has detected an issue with the gas supply and ignition and locked out the boiler to ensure it is safe.

  • Possible causes – incorrect flame detection and the F27 fault code should not be ignored as it indicates an issue with your boiler’s delicate electrical components, particularly the brains of your boiler, the printed circuit board, or PCB. The fault could be caused by moisture building up on the circuitry or other electrical parts or worn-out ignition leads which will need to be replaced.
  • The fix – if your boiler is indicating the gas supply and ignition are malfunctioning and therefore unsafe, your only option is to contact a Gas Safe engineer. You will need a qualified and experienced engineer to diagnose and resolve the problem, which could mean replacing the PCB or even installing a new boiler.

Faulty Gas Valve

The gas valve is an essential component in your heating system as it controls the heating of water for your radiators or hot water taps. When your boiler switches on and needs a flame to heat up the water, the gas valve opens up to let enough gas through for the ignition. However, a faulty gas valve is a serious malfunction as it can allow gas through even when it is not needed so never ignore the F62 error code on your boiler’s display.

  • Possible causes – a stuck or seized gas valve is the main cause of a fault in this boiler component. There could also be a wiring issue or a problem with the valve’s connection. Other causes include a failure in the printed circuit board (PCB) or a failure in the boiler itself, especially if it is an older unit.
  • The fix – as gas is involved in this common Vaillant Boiler fault, you must always call a Gas Safe registered engineer and never attempt to fix the problem yourself. Your engineer may be able to fix or replace the gas valve or other affected components. But it may be that you need to upgrade your system and get a new boiler.

Over activity

If you find your Vaillant boiler is firing up unexpectedly throughout the day, then you have an overactive boiler. This is one of the common Vaillant boiler problems, particularly with the Vaillant Ecotec Plus.

  • Possible causes – a malfunctioning thermostat or dirty air filters are the two most common causes of an overactive boiler. If a faulty thermostat indicates low temperature, it an keep the boiler running unnecessarily as it thinks the water is not being heated.
  • The fix – check the temperature and timings to see if it is set correctly and reset if necessary. If this doesn’t work, call on the services of an engineer who will be able to delve deeper into the problem and replace any faulty parts, as well as renew the air filters to get your Vaillant boiler back on track.

Which Vaillant Boiler Problems need a Heating Engineer?

While it is good to know the Vaillant error codes so you can identify a fault with your boiler, not all issues should be tackled with a little DIY. And attempting to fix certain breakdowns or faults with your boiler could actually invalidate your Vaillant warranty. To ensure your boiler fault is fixed without leaving you with an unexpected and costly bill, we’ve put together a summary list of common problems and how you should deal with them.

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Vaillant Boiler Error Codes

Just like other boiler makes, Vaillant boilers will display a fault code – a number beginning with F – on their display so you can more easily identify what may be going wrong with your system. Different issues will have a different error code so if you see an F number displayed, refer to your boiler’s manual for the full list of fault codes for that model.

How Long Should a Vaillant Boiler Last?

When buying a Vaillant boiler, their standard warranty covers between two and five years, with the option to extend up to 10 years on some products. A boiler that is 10 years or more is considered an old boiler, but if you look after your Vaillant and ensure it is serviced annually, there’s no reason it shouldn’t last longer.

How do I Reset my Vaillant Boiler?

In some error situations – a lockout, for example when your Vaillant boiler has been shut down for safety reasons – the best option is to reset your boiler. And resetting your boiler is often recommended after other faults have been repaired. By resetting your boiler, you are returning its systems back to normal working order and wiping the error code so you will get the hot water and heating back on track.

All boilers will have a reset button, so check your boiler manual for information on where it is located on your particular Vaillant model. This button will usually need to be pressed and held for a couple of seconds, then released to get everything back to normal. You will be able to tell whether your boiler has reset as the flame will ignite and the error code will disappear from the boiler’s display. There should also be a green light (rather than a red or amber).

If the boiler doesn’t reset, don’t keep pressing the reset button as this can cause further damage, but call out a Gas Safe registered engineer.

For more in-depth information on resetting your Vaillant or any other make of boiler, check out our How to Reset your Boiler guide.


  1. Most Common Boiler Problems – Vaillant
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