40 High

Daikin 40 Fault Code

The Daikin 40 fault code means: your boiler has detected that the water pressure in the system is too low for it to operate safely.. It appears on 1 Daikin model in our database.

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: Water pressure error
Typical repair cost £0-120 (including labour)

DIY fix possible

Locate the filling loop (a flexible silver hose) underneath or near the boiler.Slowly open the valves on the filling loop until you hear water moving.Watch the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar.

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Daikin models that show the 40 fault code

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

Source

Daikin 40 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 7 July 2026