BoilerFaultCodesIdeal 4Y Fault Code
The Ideal 4Y fault code means: your boiler has lost its connection to the internal thermometer that monitors water temperature, meaning it cannot safely heat your home or water.. It appears on 1 Ideal model in our database.
Technical description: Supply sensor not connected.
What causes the Ideal 4Y fault?
This fault occurs when the boiler's main computer loses communication with the temperature sensor attached to the internal pipework. It is usually caused by the sensor failing due to age, or a loose connection or damaged wire preventing the signal from reaching the control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Ideal models that show the 4Y fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4Y fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026