High Lockout
P0.1-0.4 bar on Potterton Powermax HE

Your boiler has lost water pressure and has shut itself down to prevent damage to the internal components.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Loss of pressure in heating system

What causes this 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.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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