BoilerFaultCodesTechnical description
Primary pressure over 3 bar, boiler off. Reduce CH system pressure. Check/adjust/replace primary expansion vessel
What causes this fault?
This fault occurs when the water pressure inside your heating system exceeds a safe working limit, forcing the boiler to shut down to prevent damage. The most common reason is that the internal expansion vessel, which normally absorbs the pressure of expanding hot water, has failed or lost its air charge. It can also be caused by a filling loop being left slightly open, which allows water to continuously leak into the system.
This fault is more common in winter when the heating is first turned on for long periods, as the increased heat causes water to expand and reveals issues with the 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.