BoilerFaultCodesDaikin E1-66 Fault Code
Also written as E166 — same fault.
The Daikin E1-66 fault code means: your boiler is struggling to automatically adjust its internal settings for the burner to stay lit and is attempting to restart itself.. It appears on 1 Daikin model in our database.
Technical description: Calibration condition error, wait for burner to restart
What causes the Daikin E1-66 fault?
This fault occurs when the boiler's internal computer is unable to correctly balance the mix of gas and air required for a stable flame. It often happens if the gas valve is failing to regulate flow accurately or if the sensor that monitors the flame is dirty or worn out. As a result, the system repeatedly tries to recalibrate itself to ensure safe combustion.
DIY fix possible
Reset the boiler using the front control panelWait for the boiler to complete its automatic recalibration sequenceEnsure the gas supply to the property is active
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Gas Safe Register →Daikin models that show the E1-66 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Daikin E1-66 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