BoilerFaultCodesPotterton P 3.1 Fault Code
Also written as P31 — same fault.
The Potterton P 3.1 fault code means: your boiler has reached a critically high water pressure that is unsafe for continued operation.. It appears on 1 Potterton model in our database.
Technical description: If the pressure indicated at normal working temperatures (80 °C) shows 'P 3.1 or higher, switch off the boiler and contact your service engineer.
What causes the Potterton P 3.1 fault?
This fault occurs when the water inside your central heating system expands beyond the capacity of the boiler's safety limits. The most common reason is a failure of the internal expansion vessel or a filling loop tap that has been left slightly open, causing the pressure to rise until it becomes unsafe. Because the boiler cannot safely vent this excess pressure, it shuts down to prevent damage to the internal seals and pipework.
This fault often appears when you turn your heating back on for the first time in autumn, as the thermal expansion of cold water puts immediate stress on a weakened expansion vessel.
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 P 3.1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton P 3.1 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