BoilerFaultCodesYour boiler has detected that water is not moving through the system quickly enough to prevent it from overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Insufficient primary flow
What causes this fault?
This fault occurs when the water inside the boiler heats up too quickly because it isn't being pumped away into your radiators or cylinder fast enough. The most common reasons are a failing external pump, a blockage caused by sludge in the pipework, or air trapped within the system preventing a steady flow.
This issue is more frequent in autumn when heating systems are switched back on after a long summer break, as pumps can seize and debris can settle while the system is inactive.
DIY fix possible
Check that all radiator valves are fully openEnsure the external heating pump (if visible) is runningCheck that the system water pressure is within the green zone on the gaugeReset the boiler using the selector switch
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