F20 High

Glow-worm F20 Fault Code

The Glow-worm F20 fault code means: your boiler's internal electronic components are having trouble communicating with each other because the control boards are not compatible or correctly configured.. It appears on 12 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: Interface board compatibility fault

What causes the Glow-worm F20 fault?

This fault occurs when the boiler's internal computer chips cannot speak the same language, usually after a repair where a new part has been installed. The most common reason is that the main control board and the display screen board are mismatched versions or have not been digitally 'paired' correctly. In some cases, a sudden power surge can scramble these settings, causing the components to stop recognizing each other.

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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Glow-worm models that show the F20 fault code

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

Source

Glow-worm F20 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