BoilerFaultCodesIdeal 4U Fault Code
The Ideal 4U fault code means: your boiler has stopped working because an internal temperature sensor has developed an electrical fault and can no longer read the heat levels correctly.. It appears on 1 Ideal model in our database.
Technical description: Supply sensor short-circuited.
What causes the Ideal 4U fault?
This fault occurs when the electrical resistance in the main temperature sensor drops to an abnormal level, suggesting a short circuit. The most common reason is that the sensor's internal components have perished over time, or moisture has compromised the electrical connections. Because the boiler can no longer safely monitor how hot the water is getting, it shuts down as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ideal models that show the 4U fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4U 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