F.88 High

Glow-worm F.88 Fault Code

Also written as F88 — same fault.

The Glow-worm F.88 fault code means: your boiler is struggling to keep a steady flame lit, causing it to shut down for safety.. It appears on 6 Glow-worm 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: Unstable flame (analogue input), underfloor heating contact or gas valve fault

What causes the Glow-worm F.88 fault?

This fault occurs when the boiler's control board detects that the flame is flickering or unstable, making it unsafe to continue running. The most common reasons are a buildup of carbon on the sensing probes or a failing gas valve that isn't providing a steady flow of fuel to the burner.

This fault can be more frequent during the first cold snap of winter when the boiler is suddenly forced to run at maximum output for long periods, putting strain on aging gas components.

Typical repair cost £150-350 (including labour)

Engineer required

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

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Glow-worm models that show the F.88 fault code

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

Source

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

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