BoilerFaultCodesIdeal 4L Fault Code
The Ideal 4L fault code means: your boiler has detected an electrical fault with one of its main internal temperature sensors, causing the system to shut down for safety.. It appears on 1 Ideal model in our database.
Technical description: Safety sensor short-circuited.
What causes the Ideal 4L fault?
This fault occurs when the boiler's safety sensor, which monitors for overheating, sends an abnormal electrical signal to the control board. The most common reason is that the sensor's internal wiring has failed or a moisture leak has caused a short circuit. Because this sensor is responsible for preventing the boiler from becoming dangerously hot, the system will not start until the part is replaced.
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 4L fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4L 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