F.88 High

Vaillant F.88 Fault Code

Also written as F88 — same fault.

The Vaillant F.88 fault code means: your boiler has detected an electrical connection issue with the gas valve, meaning it cannot safely ignite to provide heating or hot water.. It appears on 24 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Fault: Gas valve assembly. Gas valve assembly not connected or it is connected incorrectly, short circuit in the cable harness

What causes the Vaillant F.88 fault?

This fault occurs when the boiler's internal computer loses electrical communication with the gas valve, which is the component responsible for releasing fuel into the burner. The most common reason is a loose or damaged wiring connection between these parts, though it can also be caused by a complete electronic failure within the gas valve itself.

Typical repair cost £180-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the F.88 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant F.88 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026