Vaillant F28 Fault Code: what it is and how to fix it

Company type: Manufacturer

HQ: Remscheid, Germany

Founded: 1874

CEO: Norbert Schiedeck

The Vaillant F28 fault code will appear when the boiler is not able to ignite, and thus will not heat up the water in your heating system. Although it is not a fatal error, it requires thorough investigation by a Gas Safe engineer. As the Vaillant F28 fault code signals a problem with the gas supply, you should not attempt any DIY fixes, as this can be hazardous.

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What does the Vaillant F28 fault code tell us about the boiler?

In the manufacturer’s instructions, the Vaillant F28 fault code is officially defined as:

Code Meaning Cause
F28 Ignition fault Gas meter defective or gas pressure regulator has triggered, air in gas, gas flow pressure too low, fault on the gas valve, break in cable harness, incorrect earthing of boiler, electronics defective

What this essentially means is that the boiler is not firing up due lack of gas or broken ignition. When there is no flame, water won’t become heated, meaning your home will be left with no hot water or central heating.

The F28 can appear on the control panels of Vaillant EcoTec Pro and the EcoTec Pro Plus boilers and will display the ‘F28’ after three unsuccessful ignition attempts. At this point, your boiler will lock out. A boiler lockout is a safety measure that shuts down the boiler to protect the boiler from breaking and the user from a potential hazard.

There are several reasons why your boiler may not be igniting and may, therefore, be displaying the Vaillant F28 fault code.

Vaillant F28 Fault Code causes and fixes

Gas supply issue

The first thing to do is to check your gas supply. You can do this yourself by simply checking whether other gas appliances (for example, your gas hob) work. If none of them work, you were likely cut off for one reason or another and should contact your gas supplier directly.

If all of your other appliances work just fine, there is something wrong with the boiler itself. When diagnosing the cause of the Vaillant F28 fault code on your boiler, a registered Gas Safe Engineer will likely find faults in one of the following boiler components:

Faulty gas valve

After you call your Gas Safe engineer, they’ll most likely start by checking the gas valve. In most cases, it’s the gas valve that is the root cause of the Vaillant F28 fault code. Gas valves are part mechanical and they can sometimes get stuck. When this happens, a valve gets partially shut and the boiler won’t receive the required gas supply — this will cause it to shut down and display the Vaillant F28 fault code.

Usually, the gas valve can be freed by your engineer. However, If your gas valve needs replacing, you should expect to pay around £300 for a new component, including labour costs.

PCB fault or issue with the wiring

The PCB (printed circuit board) is the brain of your boiler, as it is electronically connected to all of the boiler’s internal components and ensures they coordinate properly. The PCB tells the gas valve when to open and close. A problem will arise if one of the wires is incorrectly connected or if there is a break in the wiring. Your engineer will be able to test each component to determine where exactly the Vaillant F28 fault code is coming from. The wiring can usually be repairable and it is usually a very simple fix.

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Faullty electrodes

The boiler uses electrodes to initially spark the gas and ignite the flame. Over time, these electrodes will suffer wear and tear and may require replacement. Therefore, even if there is gas being supplied to your boiler, faulty electrodes can result in the Vaillant F28 fault code. Your engineer will inspect the electrodes and recommend a replacement if they are indeed the problem. A replacement Vaillant electrode will cost around £25, and an ignition cable will be around £35.

Frozen condensate pipe

A condensate pipe is used to filter all of the excess water waste as vapour from the combustion process in the boiler. If the condensate pipe freezes, condensate gases will not be able to escape the system, which could lead to build up and the whole system failure. If your pipe is located outdoors, it's likely that it will freeze occasionally, especially in winter months. If you think this might be the problem, go outside and try to feel down the pipe and see if there is an area that feels colder than the rest – this could indicate a blockage or that the pipe is frozen. You can easily resolve the problem yourself by placing something hot on top of the pipe or pouring some hot water over the frozen part.

Even if you manage to resolve it, it is still worth contacting the engineer, as they will ensure this doesn't happen again. They can suggest changing the location of the condensate pipe and making it 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. He might then consider lagging and insulating the pipe with thick material to protect it against low temperatures.

Some of the newer boiler models, for example the Worcester Bosch combis, come with a CondenseSure feature to combat the problem of frozen pipes. They build up the condensed gases internally, releasing them in bulk at regular intervals, which reduces the chance of pipes freezing. This is something you might consider when purchasing a new boiler. To learn more about the Worcester Bosch combi boilers, click below.

Worcester Bosch combi boilers

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