BoilerFaultCodesYour boiler is struggling with water circulation, likely because the internal pump is not working properly or there is an air lock in the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Check diagnostic code (Page 53)
What causes this fault?
This fault occurs when the boiler detects that water isn't moving through the heat exchanger as fast as it should. The most common reasons are a failing internal pump that can no longer push the water around or a large pocket of air trapped in the system blocking the flow.
This issue is frequently seen in autumn when the heating is turned back on for the first time after summer, as pumps can seize during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like D.24 — no call-out fees, no surprises.
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Vaillant Thermocompact 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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