F28 Vaillant Fault code

Vaillant F28 Fault code – What does the error mean & how to fix it?

Vaillant boilers are one of the most popular brands in the UK so it is likely that at some point people need to know what to do when they see an F28 error code.

You should also be careful not to open the boiler’s casing or touch it yourself. This can pose a danger. It is best to have your boiler checked and repaired by a qualified Gas Safe engineer.

Officially, Vaillant defines F28 as an ignition fault. This problem could be caused by an inadequate supply of gas, a defective electrode, or an ignition lead.

The F28 fault can therefore be classified as either an ignition fault or a gas valve problem.

If this isn’t the first time you’ve mended your Vaillant boiler you may want to consider a new boiler as old boilers are much less efficient and it may be much more cost-effective in the long run.

Vaillant boiler models F28 is applicable to:

  • Vaillant Ecotec Pro
  • Vaillant Ecotec Plus,
  • Vaillant Turbomax

What does the Vaillant F28 fault code mean?

Answer: Failure during start-up: ignition unsuccessful

This means that the flame your water must pass over to heat it up before it reaches hot taps or circulates around the central heating system isn’t lit up. This error code can have many causes. To diagnose the problem and fix it, a Gas Safe registered engineer will need to come to your home.

What causes the F28 error code?

  • Gas pressure regulator or gas meter defective
  • air in gas supply
  • Gas flow pressure too low
  • The thermal isolator device has been activated.
  • Frozen condensate pipe
  • Condensate duct blocked
  • Incorrect gas restrictor
  • incorrect ET gas valve fault
  • Faulty gas valve
  • Multiple plugs on PCB wrongly plugged in
  • Break in the cable harness
  • ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective,
  • ionisation current interrupted (cable, electrode),
  • Incorrect earthing of the boiler
  • electronics defective

How to fix a F28 Vaillant error code

When it comes to sorting out and fixing the F28 fault code on a Vaillant boiler, only a few of the fixes, such as the frozen condensate pipe, can be done by the average unqualified human being. All the others will require a registered Gas Safe engineer to get your hot water back up and running.

Gas supply fault

Verify that the gas meter is not accidentally turned off. Clients are often surprised at how many times the gas lever was accidentally left in the off or partially off positions. One way to check is to make sure your payment meter is up to date and that your gas supplier hasn’t cut you off, or other gas appliances are working.

Reset your boiler

To ensure that it is not a repeat occurrence, you may have to press the reset button 3 times. You should be alert for any future problems as these may indicate that there are deeper issues with your boiler and may need to be checked by a heating professional.

Frozen condensate pipe

Make sure that your condensate pipes are not blocked or frozen in extremely cold weather. If the weather is normal, condensate pipework may become blocked due to debris or blocked paths further down.

Faulty gas valve

Another problem is the gas-valves sticking because of internal lubrication/ seals hardening under cold weather. A gas engineer must perform this procedure as it involves removing the boiler case to reach the gas valve. This is a gas-carrying item and should only be performed by a gas heating engineer.

F27 is also known to have this fault code. F27 refers to failure immediately following ignition. Vaillant F28 error, however, is a complete failure.


The gas valve’s wiring connects to the printed circuit board (PCB) via the wiring. The valve won’t be able to communicate with the PCB if the wiring is damaged or loose.

Simply put, the PCB tells the gas valve when it should open or close. The valve will not function properly without these signals. It could even close when it is being told to, causing gas supply problems.

You won’t need a new gas tank if the wiring can be repaired. It is easy to fix wires.

Printed Circuit Board (PCB).

To determine exactly what the Vaillant boiler f28 fault code means, your boiler engineer can test every component and wiring. It’s worth inspecting the PCB to make sure the gas supply and gas valve are not the problems.

The PCB is interconnected with all internal components, ensuring that the boiler runs smoothly. The boiler will shut down if it fails to give the gas valve signals to open or close.

A Gas Safe engineer will inspect the PCB and check that the wiring connecting various boiler parts to it is in good condition. A replacement of a damaged or faulty PCB can cost several hundred pounds. It may be worth buying a new boiler.

Malfunctioning Electrodes

The electrodes in your boiler ignite the gas as it flows into the boiler. These electrodes, like all boiler parts, will wear down over time. They can wear down and make it impossible to ignite the boiler.

If the problem persists, a Gas Safe registered engineer will inspect them and recommend a replacement.

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