BoilerFaultCodesPotterton P0.1-0.4 bar Fault Code
Also written as P0104BAR — same fault.
The Potterton P0.1-0.4 bar fault code means: your boiler has lost water pressure and has shut itself down to prevent damage to the internal components.. It appears on 2 Potterton models in our database.
Technical description: Loss of pressure in heating system
What causes the Potterton P0.1-0.4 bar fault?
This fault occurs when the water level inside your central heating system drops below the minimum safe threshold required for operation. The most common reasons are a slow leak from a radiator valve or pipework, or a failing internal component like the expansion vessel which helps manage pressure changes.
This issue is frequently seen in autumn when the heating is turned back on after summer, as the sudden heat can stress weakened seals or joints.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath or near the boilerSlowly open the tap or taps on the filling loop until you hear water movingWatch the pressure gauge and close the taps firmly once it reaches 1.5 bar
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Gas Safe Register →Potterton models that show the P0.1-0.4 bar fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton P0.1-0.4 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