P18 Medium

Alpha P18 Fault Code

The Alpha P18 fault code means: your boiler is struggling to maintain the correct temperature for your hot water supply, which may cause your taps or shower to run cold or fluctuate in temperature.. It appears on 2 Alpha models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: DHW reheat temp.
Typical repair cost £120-250 (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 P18 fault code

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

Source

Alpha P18 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