45 High

Alpha 45 Fault Code

The Alpha 45 fault code means: your boiler is overheating because the water is not flowing through the system as quickly as it should.. It appears on 17 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: High-temperature difference

What causes the Alpha 45 fault?

This fault occurs when the water inside the boiler heats up too quickly because it isn't being moved away into your radiators fast enough. The most common reasons are a failing external pump, a blockage in the pipework, or a buildup of debris and limescale inside the heat exchanger that restricts water flow.

This issue often surfaces in autumn when the heating is turned back on after a long summer break, as external pumps can seize up during periods of inactivity.

Typical repair cost £120-£350 (including labour)

DIY fix possible

Check that all radiator valves (TRVs) are fully openEnsure the external system pump is running and hasn't seizedCheck for any blockages in the system filters

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Alpha models that show the 45 fault code

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

Source

Alpha 45 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