BoilerFaultCodesYour boiler has detected an issue with an external safety device or thermostat connection, causing it to stop running for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: External device fault (UHT/CPA)
What causes this fault?
This fault occurs when an external safety component, such as an underfloor heating limit thermostat, detects an unsafe temperature and breaks the electrical circuit to the boiler. It can also be caused by a loose connection or a fault within the internal wiring harness that prevents the control board from seeing a complete safety loop.
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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