H9-01 Low

Daikin H9-01 Fault Code

Also written as H901 — same fault.

The Daikin H9-01 fault code means: your boiler is struggling to understand the outdoor temperature, which may cause your heating to run less efficiently or at the wrong temperature.. 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: Outside sensor fault – try resetting the boiler

What causes the Daikin H9-01 fault?

This fault occurs when the boiler loses its connection to the probe located on the outside of your house designed to monitor weather conditions. The most common reason is that moisture or corrosion has damaged the sensor's internal wiring, or the electrical signal between the sensor and the boiler's main control board has been interrupted.

This issue often comes to light during the first cold snap of autumn when the boiler attempts to use outdoor temperature data to adjust your heating for the winter.

Typical repair cost £90-160 (including labour)

DIY fix possible

Locate the reset button (usually a circular arrow or 'R') on the front control panel.Press and hold the reset button for 2 to 3 seconds.Wait for the boiler to restart; if the code reappears, a professional is required to check the wiring.

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Daikin models that show the H9-01 fault code

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

Source

Daikin H9-01 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