20 High

Alpha 20 Fault Code

The Alpha 20 fault code means: your boiler is struggling to detect the flame needed to heat your water, even if the burner has successfully lit.. It appears on 23 Alpha 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: Flame sensing fault

What causes the Alpha 20 fault?

This fault occurs when the boiler's control system cannot confirm that a flame is present, even if the burner is actually firing. The most common reason is a buildup of carbon or debris on the monitoring probe, or a loose electrical connection that prevents the signal from reaching the main control board.

Typical repair cost £90-250 (including labour)

Engineer required

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

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Alpha models that show the 20 fault code

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

Source

Alpha 20 fault code information on this page is sourced and cross-checked against the official Alpha service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026