BoilerFaultCodesYour boiler is struggling to correctly flow water through the system, which is preventing it from heating up properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Diaphragm
What causes this fault?
This fault occurs when the rubber diaphragm inside the diverter valve perishes or tears, preventing the boiler from detecting when you turn on a hot tap. Because the internal mechanism cannot move correctly to divert heat, the boiler fails to fire up even though the water is running. Over time, the rubber naturally loses its elasticity or develops pinholes due to constant stretching and contact with system debris.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like A9 — no call-out fees, no surprises.
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Worcester Bosch WR325 RSF is discontinued — time for a new one?
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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