U4-65 Low

Daikin U4-65 Fault Code

Also written as U465 — same fault.

The Daikin U4-65 fault code means: your boiler is still providing heat and hot water, but it has lost communication with your smart room thermostat, meaning you cannot control the temperature remotely.. It appears on 1 Daikin model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: OpenTherm room thermostat connection is defective – your boiler will continue to operation but the thermostat is out of operation

What causes the Daikin U4-65 fault?

This fault occurs when the digital conversation between your boiler and your smart thermostat is interrupted, usually due to a loose wire or a failing electronic component in the control box. The most common reason is a break in the physical communication cable or a software glitch in the thermostat receiver that prevents it from sending instructions to the boiler.

Typical repair cost £80-180 (including labour)

DIY fix possible

Check that your room thermostat has power and functional batteries.Ensure the thermostat bridge or receiver is plugged in and switched on.Inspect the wiring connection between the thermostat wall plate and the boiler for any loose cables.

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Daikin models that show the U4-65 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Daikin U4-65 fault code information on this page is sourced and cross-checked against the official Daikin service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026