BoilerFaultCodesAlpha d7 Fault Code
Also written as D7 — same fault.
The Alpha d7 fault code means: your boiler is struggling to read the temperature of the incoming water or the water stored in your hot water cylinder, which may result in inconsistent heating or hot water performance.. It appears on 9 Alpha models in our database.
Technical description: Mains inlet temperature or FlowSmart cylinder temperature (if sensor fitted) °C
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 d7 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Alpha d7 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