BoilerFaultCodesPotterton D(2) Fault Code
Also written as D2 — same fault.
The Potterton D(2) fault code means: your boiler's gas valve is not closing properly because of debris, which could lead to an unsafe gas buildup within the unit.. It appears on 1 Potterton model in our database.
Technical description: Dirt on valve seat of Honeywell control.
What causes the Potterton D(2) fault?
This fault occurs when microscopic debris or grit becomes trapped within the gas valve mechanism, preventing it from forming a tight seal when the boiler switches off. Because the valve cannot close fully, a small amount of gas continues to leak into the combustion chamber, which creates a significant safety risk. The most common reason is the age of the internal components or particulates entering from the gas supply pipework.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Potterton models that show the D(2) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton D(2) fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026