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Vaillant Boiler F28 Fault Code [Causes & Repair Advice]

If you’re having problems with your Vaillant boiler and it’s showing the F28 fault code, this guide has everything you need to know.

Below we’ll cover the common causes of the F28 error code being displayed, and what to do next.

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Clearing The F28 Fault Code

This isn’t a fix you should be attempting yourself. Call a Gas Safe engineer to find and fix the problem.

Working on boilers is dangerous. In this case, this is a potential gas flow or valve problem, and that’s even more dangerous than usual.

Get help from repair engineers here, they’ll be able to offer help and advice, then fix the error code on your Vaillant boiler.

Why The F28 Fault Code is Being Displayed

The F28 fault code will be displayed on Vaillant EcoTec boilers when 3 ignition attempts have been unsuccessful.

At this stage your boiler will lockout. In order to get your boiler up and running again, a Gas Safe engineer will need to rectify the problem, and then go through the reset procedure.

What Causes The F28 Error

Generally, the F28 error is going to be grouped into one of two categories:

  • Gas valve faults
  • Gas supply faults.

More specifically, that’s going to mean checking the:

  • Wiring harness to the gas valve / gas valve is mechanically sound
  • Meter’s regulator
  • Condensate pipe
  • Printed circuit board (PCB).

On rare occasions, things such as air in the gas supply can also be to blame.

How To Fix The Vaillant F28 Fault Code

There are a few things your engineer is going to check to determine what the cause of the F28 error code being displayed is, and their next steps.

  1. Gas Valve

After calling a Gas Safe engineer, it’s most likely they’ll start by checking the gas valve. It’s the gas valve that is the root cause of the F28 fault code most of the time.


The wiring on the gas valve connects the valve with the printed circuit board (PCB). If the wiring is loose or damaged, it’s not going to communicate correctly with the PCB.

Put simply, the PCB tells the gas valve when to open and close. Without those signals, it’s not going to function correctly; it could be closed even when the PCB is telling it to open, causing a gas supply fault.

If wiring isn’t beyond repair, you’ll not need a new gas valve, and instead, it’s a quick fix.

Valve Function

Gas valves are part mechanical and part electrical. Like any mechanical parts, they can wear or seize over time.

Typically, gas valves tend to get stuck, rather than wear out. That’s going to mean even if it’s trying to open, it might be seized partially shut. Again, that’s not going to provide the gas supply needed – your boiler will simply shut down, and display the F28 fault code.

If the gas valve isn’t ridiculously worn and your engineer can free it, it can be reused.

Gas Valve Replacement Cost

As we’ve detailed in our guide to boiler gas valves, you should expect to pay around £300 for a new component. That’s going to include parts and labour.

  1. Gas Meter Regulator

Gas meter regulator faults aren’t as common as valve problems, but they can still occur.

Your boiler repair engineer is going to need to check the regulator isn’t frozen (only if the meter is located outside), blocked, or faulty.

If it is, this is going to restrict the flow of gas from the meter into your property and mean that gas pressure to your boiler is too low.

The boiler will struggle to ignite with low gas pressure, and eventually will lockout as well as displaying the F28 fault code.

  1. Condensate Blockage

Like the meter’s regulator, the condensate can get blocked. If it does, it’s not going to allow condensed flue gases to escape, and that’s dangerous. Your boiler’s fault finding system knows this and is going to immediately lockout the boiler, then display the F28 fault code.

Typically, blocked condensate pipes occur in winter. The condensed flue gases in the pipe freeze over.

The pipe can be thawed out, but your engineer needs to ensure this doesn’t happen again. The easiest way to make this happen is to route the condensate pipe as close to vertical as possible.

This is going to reduce the time the condensed gases are in the pipe, and therefore, the chances of them freezing. After this, they’ll also want to lag the pipe to protect it from the elements.

Newer boilers from certain brands (like the Worcester boilers here), have a CondenseSure to combat this exact problem. They build up the condensed gases internally, releasing them in bulk at regular intervals, which reduces the chance of a freeze over.

  1. Printed Circuit Board

Your boiler engineer will be able to test each component in your boiler (and its wiring) to determine where the problem lies. If the gas supply and gas valve aren’t the culprits, it’s worth checking the PCB.

The PCB works with all internal components ensuring the boiler works smoothly. If it malfunctions in any way, for instance, stops giving the gas valve signals to open and close, the boiler will shut down and show the F28 fault code.

What’s Next?

Thanks for reading our guide to the Vaillant EcoTec F28 fault code. If you’re looking for information on other error codes, jump over to our guide covering Vaillant boiler problems or directly the f61 fault code for vaillant boilers.

Still got questions? Drop us a line via our contact form and we’ll do our best to help you out.

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