BoilerFaultCodesPotterton P3.0-3.5 bar Fault Code
Also written as P3035BAR — same fault.
The Potterton P3.0-3.5 bar fault code means: your boiler has shut down because there is too much water pressure in the system, which could lead to leaks if not addressed.. It appears on 2 Potterton models in our database.
Technical description: Pressure too high, boiler off
What causes the Potterton P3.0-3.5 bar fault?
This fault occurs when the water pressure inside your heating system exceeds the safe operating limit of 3.0 bar. The most common reasons are a filling loop valve being left slightly open or the internal expansion vessel losing its air charge, which prevents it from absorbing the natural expansion of water as it heats up.
This issue often surfaces during the first cold spell of autumn when the heating is turned on for the first time in months, causing the water to expand and reveal a failing 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 until it returns to between 1.0 and 1.5 barPress the reset button to restart the boiler
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Gas Safe Register →Potterton models that show the P3.0-3.5 bar fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton P3.0-3.5 bar 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