Vaillant F28 Error/Fault Code - How To Fix

Any time your boiler displays an error code, it can be a huge stressor, especially if it degrades the performance of your heating system, ESPECIALLY in the freezing, winter period!

In this blog we’re going to be exploring the pesky F28 error code for Vaillant boilers, including what this means, what’s the cause and the best way to solve the problem.

Error Codes Explained

A boiler error code displays an alphanumeric three digit fault detection message (e.g. F28) when the system detects an error such as an integrated component not functioning as it should.

Error codes are found on the boiler's digital display screen, located front and centre on the unit itself or at the bottom of the casing, sometimes covered by a plastic folding panel.

Vaillant F28 Meaning

Officially, the Vaillant F28 code signals an ignition fault, this problem can be complex due to the fact it can be caused by several internal issues, The F28 warning code will be emitted if the boiler fails three ignition attempts.

The broad list of potential causes mean the F28 can be, in a wider sense, categorised as a gas valve issue as well as an ignition problem.

Ignition is required to light the gas, creating the flame which heats the cold water that runs over it, thereby providing the property with a supply of hot running water; a gas valve controls the flow of gas within the boiler.

An F28 error code can result in a boiler ‘lockout’ (shutdown to prevent further fault). We understand the desire to get your central heating system up and running by simply restarting your boiler, but just hang on if possible!

Carrying out assessments and diagnosing the cause of the issue can be hugely beneficial in the long run and can enable the issue to be completely remedied, rather than half fixed, potentially leading to further breakdowns.

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F28 Causes

Mechanical Fault With The Gas Valve

The valve, which opens and closes to meet the boiler's gas demands, may begin to stick over time due to natural wear and tear, especially if the boiler is an older model, impairing overall heating functionality.

Frozen Condensate Pipe Causing A Blockage

A condensate pipe transfers ‘condensate’ or wastewater by-products, from a boiler to the outside of a property, usually depositing it in a sewage system.

A condensate pipe may become blocked or obstructed due to cold weather causing the pipe to freeze, this can negatively impact a boiler's performance when you need heat the most.

How To Thaw Out A Frozen Condensate Pipe

The most common way to thaw out a frozen part of the condensate pipe, is to pour warm water over the outside of the piping, but be careful as not to cause a slip hazard. Also don't pour boiling water on the pipe, let this cool down for 10 minutes first.

Alternatively, you can place a hot water bottle on the affected area or have the above ground part of the piping lagged (insulated).

Electrical (Wiring) Fault

Boiler components are connected electronically to the PCB (printed circuit board), this is the control centre responsible for regulating the coordination of several integrated components.

If any wiring or circuitry is poorly connected between the gas valve and PCB, the signals will no longer be effectively transmitted, resulting in valve malfunction and a boiler ‘lockout’.

Low Boiler pressure

Low boiler pressure could be caused by several occurrences such as:

Water leak in key pipework area
Pressure relief valve that has been left open
Radiators been inefficiently bled
Not enough water entering system
Broken or condemned boiler

If your boiler is suffering from low pressure, check out our handy troubleshooting guide!

And if you’re thinking of upgrading to a more efficient model, our 2025 comparison on what is the best combi boiler covers the top-performing options for UK homes.

Fixing The F28 Error Code

The issues discussed above that may be the potential cause of the F28, can be complex heating issues that if improperly handled could lead to further boiler problems or health risks.

It’s always wise to organise an expert, Gas Safe registered engineer to undertake any substantial boiler work!

Gas Safe Registered Engineer

This is a fully trained and qualified gas engineer who is legally licensed under the published Gas Safety (Installation and Use) Regulations 1998 (GSIUR).

The Gas Safe Register is the appointed representative of the safety regulatory group- Health and Safety Executive. All of our iHeat engineers are registered Gas Safe!

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Servicing

Arranging for your boiler to be annually checked over or ‘serviced’ by a qualified engineer can be a fantastic way of analysing the state of your heating system in yearly increments, identifying and rectifying any faults before they have a chance to progress.

iHeat

iHeat provides expert boiler installation services and troubleshooting support for issues like the Vaillant F28 error code. Our team is dedicated to helping you maintain a reliable heating system, whether you’re upgrading to a new boiler or resolving common faults.

If you’re considering replacing your current boiler, take a look at our full guide to new boiler cost for average prices and installation details across the UK in 2025.

Boiler Servicing

At iHeat all of our subcontracted engineers are Gas Safe registered and can service your boiler swiftly and safely. Prices of an expert boiler service with iHeat start from £99.These figures might fluctuate regionally and can also depend on the specific type of boiler you own, such as a combi, gas, or oil boiler.

Not sure which make to choose next? Our guide to the best boiler brands highlights the most reliable and energy-efficient models available in the UK right now.

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