BoilerFaultCodesYour boiler has detected that water is not circulating fast enough through the system, usually due to a lack of water pressure or a blockage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: All Boilers
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is moving too slowly or not at all, which risks the unit overheating. The most common reasons are a build-up of sludge blocking the pipes, a failing internal pump, or simply that the system pressure has dropped too low to maintain flow.
This issue is more frequent in autumn when the heating is first turned on after summer, as stationary pumps can seize and debris may have settled in the pipes.
DIY fix possible
Check the pressure gauge and ensure it is between 1 and 1.5 barIf pressure is low, use the filling loop to top up the water levelBleed any trapped air from your radiatorsPress the 'Reset' button on the boiler control panel
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A boiler cover plan would cover faults like 104 — 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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