BoilerFaultCodesTechnical description
A pressure of 3 or greater indicates a fault. The safety pressure relief valve will operate.
What causes this fault?
This fault occurs when there is too much water pressure in the system, often caused by the filling loop being left slightly open or a internal leak between the domestic hot water and central heating sides. It can also happen if the expansion vessel has lost its air charge, meaning there is no room for water to expand as it heats up. As a result, the pressure rises rapidly until it forces the safety valve to open and discharge water.
This issue often becomes apparent in winter when the heating is first turned on, as the increased heat causes water to expand and reveals a failing expansion vessel.
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.