BoilerFaultCodesTechnical description
If the pressure indicated at normal working temperatures (80 °C) shows 'P 3.1 or higher, switch off the boiler and contact your service engineer.
What causes this fault?
This fault occurs when the water inside your central heating system expands beyond the capacity of the boiler's safety limits. The most common reason is a failure of the internal expansion vessel or a filling loop tap that has been left slightly open, causing the pressure to rise until it becomes unsafe. Because the boiler cannot safely vent this excess pressure, it shuts down to prevent damage to the internal seals and pipework.
This fault often appears when you turn your heating back on for the first time in autumn, as the thermal expansion of cold water puts immediate stress on a weakened expansion vessel.
Engineer required
This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.