Vaillant F28 Fault: Causes & How to Fix It

If your Vaillant boiler is showing an F28 fault, it means the boiler has failed to ignite and has entered lockout after several attempts.

Gas supply is only one possible cause — the fault can also involve a frozen condensate pipe, the gas valve, PCB or wiring, and will need a Gas Safe engineer to diagnose safely if basic checks don't clear it.

This guide explains what the Vaillant F28 fault means, the most common causes, and what you can safely check before arranging a repair.

What Does the Vaillant F28 Fault Mean?

The Vaillant F28 fault is an ignition failure.

The boiler has attempted to light several times but could not establish a flame, so it locks out to protect the appliance.

Start by checking whether other gas appliances in your property are working.

• If none of them work, the issue is likely with your gas supply.
• If they do work normally, the fault is probably inside the boiler.

During very cold weather, frozen condensate pipes are another common cause of this error.

Avoid repeatedly resetting the boiler without finding the cause. If the fault remains after a single reset, arrange a proper inspection — resetting again rarely solves an ignition fault on its own.

Common Causes of the Vaillant F28 Fault

The most common causes include:

• interrupted gas supply
• faulty gas valve
• frozen or blocked condensate pipe
• damaged wiring
• ignition component failure
• faulty PCB (printed circuit board)

All of these prevent the boiler from igniting correctly.

How to Fix the Vaillant F28 Fault

Reset the boiler

A single reset may clear a temporary ignition fault. If the F28 code immediately returns, further investigation is needed.

Check the condensate pipe

In freezing weather the condensate pipe can freeze, preventing the boiler from operating normally.

If you can safely reach the external pipe, carefully thaw it using warm (not boiling) water. If you're unsure, leave this to an engineer.

Check the gas supply

Make sure your gas supply is available. Check another gas appliance such as a hob. If you have a prepaid meter, confirm there is enough credit.

If other appliances have no gas supply, contact your supplier rather than resetting the boiler repeatedly.

Inspect the gas valve

A sticking or failed gas valve can stop gas reaching the burner. Replacement usually requires a Gas Safe engineer and should never be attempted by a homeowner.

Check the PCB and power supply

Check that the boiler has electrical power and that no fuse or breaker has tripped. If power is present, a failed PCB could prevent the ignition sequence from completing.

Inspect the wiring

Loose or damaged wiring between the PCB, ignition components and gas valve can also trigger an F28 fault. This requires testing by a qualified engineer.

If your boiler is showing a different error, see our complete guide to Vaillant boiler fault codes for explanations of the most common fault codes.

Preventing Future F28 Faults

Although not every F28 fault can be prevented, regular maintenance reduces the chances of unexpected breakdowns. Good practice includes:

• annual boiler servicing
• keeping the condensate pipe protected during winter
• arranging repairs as soon as faults appear
• using a Gas Safe registered engineer

Small problems are usually cheaper to repair before they develop into larger faults.

Need Help With a Vaillant F28 Fault?

If your boiler still shows the F28 fault after checking the gas supply and carrying out a single reset, it's time to arrange a professional inspection.

Our Gas Safe engineers diagnose ignition faults across London, including gas valve faults, PCB failures, wiring problems and frozen condensate pipes. If the fault returns after basic checks, our boiler repair in London service can diagnose and repair the problem safely. We'll identify the cause and get your heating and hot water working again as quickly as possible.