27 High

Alpha 27 Fault Code

The Alpha 27 fault code means: your boiler has detected that water is not moving through the system quickly enough to prevent it from overheating.. 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: Insufficient primary flow

What causes the Alpha 27 fault?

This fault occurs when the water inside the boiler heats up too quickly because it isn't being pumped away into your radiators or cylinder fast enough. The most common reasons are a failing external pump, a blockage caused by sludge in the pipework, or air trapped within the system preventing a steady flow.

This issue is more frequent in autumn when heating systems are switched back on after a long summer break, as pumps can seize and debris can settle while the system is inactive.

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

DIY fix possible

Check that all radiator valves are fully openEnsure the external heating pump (if visible) is runningCheck that the system water pressure is within the green zone on the gaugeReset the boiler using the selector switch

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Alpha models that show the 27 fault code

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

Source

Alpha 27 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