BoilerFaultCodesIdeal F04 Fault Code
The Ideal F04 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, which means it cannot heat your home or water safely.. It appears on 3 Ideal models in our database.
Technical description: Flow Thermistor Fault
What causes the Ideal F04 fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the heat of the water leaving the unit. It is usually caused by the internal components of the sensor failing over time or a loose connection in the electrical wiring that links the sensor to the main computer.
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 F04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal F04 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