How much does it cost to fix Ideal error code 4Y?

Typical repair cost for the Ideal 4Y fault is £90-180 including labour.

4Y High

Ideal 4Y Fault Code

Q: What does the Ideal 4Y fault code mean?

Your boiler has lost its connection to the internal thermometer that monitors water temperature, meaning it cannot safely heat your home or water.

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.

Typical repair cost £90-180 (including labour)

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.

Maximiser SE Repair: £90-180

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 27 April 2026