91 High

Alpha 91 Fault Code

The Alpha 91 fault code means: your boiler is trying to start but cannot detect the flame, so it is shutting down for safety reasons to prevent gas buildup.. It appears on 10 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: Block - flame signal lost during ignition. The flame signal is lost repeatedly during ignition
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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Alpha models that show the 91 fault code

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

Source

Alpha 91 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 27 April 2026