43 High

Alpha 43 Fault Code

The Alpha 43 fault code means: your boiler has lost the signal that confirms a flame is burning, so it has shut down for safety.. It appears on 22 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: Loss of flame rectification

What causes the Alpha 43 fault?

This fault occurs when the boiler's control board can no longer detect the electrical signal that confirms a flame is present inside the burner. The most common reason is that the sensing probe has become coated in carbon deposits or has worn out, preventing it from 'seeing' the flame even if the boiler has actually ignited. In some cases, it can also be caused by an unstable gas supply or a moisture build-up on the electrical leads.

Typical repair cost £120-280 (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 43 fault code

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

Source

Alpha 43 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 31 August 2026