d6 Low

Alpha d6 Fault Code

Also written as D6 — same fault.

The Alpha d6 fault code means: the boiler is struggling to read the outdoor temperature from a sensor installed outside your home, so it is using a default setting to keep your heating running.. 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: External weather compensation probe temperature (value flashes if negative) °C
Typical repair cost £100-180 (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 d6 fault code

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

Source

Alpha d6 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