d4 Low

Alpha d4 Fault Code

Also written as D4 — same fault.

The Alpha d4 fault code means: your boiler is notifying you that the current temperature setting for your radiators is being communicated to the system, which is a normal status indication rather than a fault.. It appears on 9 Alpha models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Central heating set point temperature

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 d4 fault code

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

Source

Alpha d4 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