BoilerFaultCodesPotterton P3.0-3.5 Fault Code
Also written as P3035 — same fault.
The Potterton P3.0-3.5 fault code means: your boiler has shut down because there is too much water pressure in the central heating system.. It appears on 1 Potterton model in our database.
Technical description: Primary pressure over 3 bar, boiler off. Reduce CH system pressure. Check/adjust/replace primary expansion vessel
What causes the Potterton P3.0-3.5 fault?
This fault occurs when the water pressure inside your heating system exceeds a safe working limit, forcing the boiler to shut down to prevent damage. The most common reason is that the internal expansion vessel, which normally absorbs the pressure of expanding hot water, has failed or lost its air charge. It can also be caused by a filling loop being left slightly open, which allows water to continuously leak into the system.
This fault is more common in winter when the heating is first turned on for long periods, as the increased heat causes water to expand and reveals issues with the expansion vessel.
DIY fix possible
Check that the silver filling loop valves are tightly closedBleed water from a radiator using a bleed key to reduce pressureMonitor the pressure gauge to ensure it returns to between 1 and 1.5 barPress the reset button once the pressure is stabilised
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Gas Safe Register →Potterton models that show the P3.0-3.5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton P3.0-3.5 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