How to Fix a Vaillant F27 Fault Code

The Vaillant F27 fault code means the boiler has detected an incorrect flame signal. It is most commonly seen on Vaillant ecoTEC Pro and ecoTEC Plus boilers and usually causes the boiler to lock out as a safety precaution.

What Does the Vaillant F27 Fault Code Mean?

An F27 fault points to a problem with flame detection or the components that control ignition and combustion. Because it affects the boiler's safety systems, the appliance shuts down until the fault has been diagnosed and repaired.

Common Causes of a Vaillant F27 Fault

The most common causes are:

• Moisture affecting electrical components
• Faulty gas valve
• Failed ignition leads or spark electrodes
• PCB failure
• Dirty or faulty flame sensor

Several faults can produce the same error code, so replacing parts without testing can become expensive.

How to Fix a Vaillant F27 Fault Code

Carry out one boiler reset using Vaillant's recommended procedure. If the F27 fault returns, avoid repeatedly resetting the boiler.

A Gas Safe engineer should diagnose the cause before any parts are replaced. Depending on the fault, repairs may involve the flame sensor, ignition components, gas valve or PCB.

If your boiler is older and needs major parts, it may be worth comparing the repair cost against a replacement.

Can You Reset or Fix an F27 Fault Yourself?

A single reset is reasonable if recommended in the user manual.

Beyond that, no. The F27 fault relates to combustion and gas safety. Any diagnosis or repair should be carried out by a Gas Safe registered engineer.

Does the Vaillant Warranty Cover an F27 Fault?

Warranty cover depends on what caused the fault.

Manufacturing defects may be covered if the boiler remains within its warranty period. Wear and tear, lack of servicing or external damage generally are not.

When to Call a Gas Safe Engineer

Arrange an engineer if:

• The F27 fault returns after resetting.
• The boiler keeps locking out.
• Heating or hot water has stopped.
• You suspect a fault with the flame sensor, gas valve or PCB.

If the fault keeps returning after a reset, book a Vaillant boiler repair in London and we'll diagnose the problem safely.

If you're seeing a different error code, check our guide to Vaillant boiler fault codes to identify the cause before arranging a repair.

Need Help With a Vaillant F27 Fault?

Book a Gas Safe engineer today. We'll diagnose the fault, explain what's causing it and provide a fixed quotation before carrying out any additional repair work.