BoilerFaultCodesYour boiler has stopped to prevent overheating because it cannot move water through the system properly or there is an air pocket trapped inside.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Exchanger protection intervention – could be because no system water circulation or there’s air in the system
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heat isn't leaving the heat exchanger fast enough, causing a rapid rise in temperature. This is usually caused by a pump failure that stops water from moving or a large air bubble trapped in the pipework that blocks the flow. In some cases, a significant buildup of sludge or a closed valve can also prevent the necessary circulation.
This issue often appears when the heating is first turned on after summer, as pump components can seize up during long periods of inactivity.
DIY fix possible
Check the central heating pressure gauge is between 1 and 1.5 barBleed all radiators to remove trapped airTry resetting the boiler using the 'R' button
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A boiler cover plan would cover faults like F43 — 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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