4 / Y High

Ideal 4 / Y Fault Code

Also written as 4Y — same fault.

The Ideal 4 / Y fault code means: your boiler's temperature-sensing component is not registering a signal, meaning the system has stopped operating to prevent overheating.. It appears on 1 Ideal 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: Supply sensor not connected.
Typical repair cost £120-220 (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 4 / Y fault code

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

Source

Ideal 4 / Y 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