BoilerFaultCodesYour boiler has detected an internal computer error that is preventing it from running safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Internal fault
What causes this fault?
This fault occurs when the boiler's internal computer experiences a critical communication failure or a malfunction in its electronic memory. It typically happens when the main circuit board can no longer verify its own safety settings, causing the system to shut down to prevent unpredictable behavior.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like b5 — no call-out fees, no surprises.
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Viessmann Vitodens 100 Compact 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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