BoilerFaultCodesWhat the manual says
Manufacturer manualHigh water pressure (above 2.8 bar)
What causes this fault?
This fault occurs when the water pressure inside your system rises beyond safe operating levels, often caused by a filling loop being left slightly open or a failure in the internal expansion vessel. When the vessel can no longer absorb the natural expansion of heated water, the pressure spikes and triggers an automatic safety shutdown. In some cases, it can also be caused by a faulty internal valve allowing fresh mains water to constantly leak into the heating circuit.
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 exposes any underlying issues with the expansion vessel.
DIY fix possible
Check that the silver braided filling loop valves are fully closedLocate a radiator and bleed water from it using a radiator key to lower the pressureMonitor the pressure gauge until it returns to between 1.0 and 1.5 barPress the reset button to clear the fault code
Avoid the next call-out bill
A cover plan would handle faults like P20: no call-out fees, no surprise bills.
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