BoilerFaultCodesYour boiler has too much water in the system, which puts extra stress on the internal components and may cause it to shut down for safety.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: High 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
Locate the filling loop valves under the boiler and ensure they are tightly closed.Bleed water from a radiator using a radiator key until the pressure gauge on the boiler drops to between 1.0 and 1.5 bar.Restart the boiler to see if the fault code clears.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like P20 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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