BoilerFaultCodesYour boiler's computer cannot find the physical security chip it needs to know which model it is, preventing the system from starting.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Keyed plug not detected.
What causes this fault?
This fault occurs when the boiler's main control board loses communication with a small, physical security chip called a code plug. Usually, this is caused by the plug vibrating loose over time or the electronic internal memory on the chip failing, leaving the boiler unable to identify its own safety settings.
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 b1 — no call-out fees, no surprises.
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Worcester Bosch ZB 7 27 HE 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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