BoilerFaultCodesIdeal E4 Fault Code
The Ideal E4 fault code means: your heat pump has stopped making hot water because the sensor that monitors your cylinder's temperature is no longer communicating correctly.. It appears on 2 Ideal models in our database.
Technical description: DHW Cylinder Thermistor (T5) Error
What causes the Ideal E4 fault?
This fault occurs when the main control board loses the electrical signal from the sensor inside your hot water tank. This usually happens because the sensor has failed internally due to age or because the wiring connecting the tank to the heat pump unit has become loose or damaged. Without this information, the system shuts down as a safety precaution because it cannot monitor how hot the water is getting.
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 E4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal E4 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