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Vaillant Boiler F28 Fault Code [Causes & Repair Advice]

If you’re getting the F28 Vaillant boiler fault code, this guide has everything you need to know. We’ll cover the common causes of the Vaillant boiler F28 error code, and provide a list of possible solutions.

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Clearing the Vaillant Boiler F28 Fault Code

First things first — working on boilers is dangerous, and the F28 Vaillant boiler error code usually points to a problem with the gas supply, which makes DIY fixes an even greater hazard. Meaning, this isn’t a fix you should ever attempt by yourself. Call a Gas Safe engineer to find and fix the problem.

Get help from repair engineers here; they’ll be able to offer help and advice, then fix the F28 code on your Vaillant boiler.

Why the Vaillant F28 Fault Code is Being Displayed

Vaillant EcoTec and Turbomax Plus 824/828E boilers all display “F28” after 3 unsuccessful ignition attempts.

At this stage, your boiler will lock out. 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 Vaillant Boiler Error

Although F28 is technically an ignition fault, there are several underlying issues that may cause it. Generally, though, problems behind the F28 Vaillant fault code can be grouped into 1 of 2 categories:

  • Gas valve faults
  • Gas supply faults

More specifically, this means inspecting 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 F28 Vaillant Boiler Fault Code

There are a few things your engineer may check to determine the cause of the F28 boiler fault, and determine the next steps.

  1. Gas Valve

After you call a Gas Safe engineer, they’ll most likely start by checking the gas valve. It’s the gas valve that is the root cause of the F28 boiler 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, the valve can’t communicate correctly with the PCB.

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

If wiring is repairable, you’ll not need a new gas valve; and fixing wires a quick fix.

Valve Function

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

That said, typically, gas valves tend to get stuck, rather than wear out. And when a valve gets partially shut, the boiler won’t receive the required gas supply —  this will cause it to 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 includes 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 will need to make sure that the regulator isn’t frozen (only if the meter is located outside), blocked, or faulty.

If it is, it will restrict the flow of gas from the meter into your property and reduce the gas pressure to your boiler.

The boiler will struggle to ignite with low gas pressure, and eventually lock out, leaving you with an F28 on the boiler display.

  1. Condensate Blockage

Like the meter’s regulator, the condensate pipe can get blocked. If it does, it won’t allow condensed flue gases to escape, and that’s dangerous. Your boiler’s fault finding system knows this and is going to immediately lock out the boiler and alert you with an F28.

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 will 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 feature 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 (PCB) and Wiring Faults

Your boiler engineer will be able to test each component in your boiler (and its wiring) to determine where the F28 boiler fault is coming form. 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.

You’ll need a Gas Safe engineer to inspect the PCB for damage, and also check if the wiring that connects various boiler parts to the PCB is in good working order. Replacing a faulty PCB might set you back several hundred pounds, so at this stage, it may be worth investing in installing a new boiler altogether.

  1. Malfunctioning Electrodes

Your boiler uses electrodes to ignite the gas as it flows in. Over time, these electrodes suffer wear and tear like any other boiler part. If they wear out, ignition becomes impossible and your boiler shows you “F28”.

You Gas Safe engineer will inspect the electrodes and recommend a replacement if they are indeed the problem.

  1. No Gas to Your Property

Remember how we urged you to leave the F28 to a Gas Safe engineer? Well, here’s an exception to the rule. Seeing F28 on a boiler may mean that there’s no gas being supplied to your property — and you can check this by trying to turn on other gas appliances in your home.

If you find that your range or fireplace aren’t lighting up, chances are that your gas supply has been switched off for one reason or another. In this event, the best thing to do is call your gas supplier and ask for an explanation.

Boiler Still Not Working?

Boilers that are still not working after you’ve attempted repairs (or those that break down often) are usually due for a replacement. You can get a new boiler quote from Heatable on your screen in only 90 seconds by filling in an anonymous questionnaire.

Heatable boiler fitting cost

What’s Next?

Thanks for reading our guide to the F28 Vaillant boiler 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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