High Lockout
U4-67 on Daikin D2CND

Your boiler has experienced a communication error that has stopped it from working, and it requires a manual power reset to clear the internal memory.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Remote reset supervision, switch off the power at the mains – if problem repeats Contact a heating engineer

What causes this fault?

This fault occurs when the boiler's internal computer loses track of its safety checks and needs to clear its temporary memory. The most common reason is a brief disruption in communication between the main control board and the display, or an electrical glitch that causes the software to stall. If a power reset doesn't work, it usually indicates that the wiring has come loose or the electronic circuit board is failing.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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