BoilerFaultCodesYour boiler has too much water inside its system, which can put unnecessary stress on the pipes and seals.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: Water pressure too high
What causes this fault?
This fault occurs when the internal water pressure exceeds safe operating limits, often because the filling loop used to top up the system has been left slightly open or is leaking. It can also happen if the expansion vessel, which manages heat-related water expansion, has failed or lost its air charge. As the water heats up and expands with nowhere to go, the pressure rises until the boiler shuts down to protect its internal components.
DIY fix possible
Locate a radiator bleed valve and use a key to slowly release water into a cloth or container.Monitor the pressure gauge on the boiler front until it drops back into the green zone (usually 1.0 to 1.5 bar).Ensure the blue or black filling loop valves under the boiler are tightly closed to prevent more water from entering.
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F40 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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