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 the internal water pressure becomes too high, often because the expansion vessel has lost its air charge and can no longer absorb the natural expansion of heated water. It can also be caused by a filling loop being left slightly open, which allows water from the mains to constantly leak into the system, or a split heat exchanger allowing cross-contamination.
This issue is most frequently noticed in winter when the heating is first turned on, as this is when the water undergoes the most expansion and puts the most stress on the 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.