BoilerFaultCodesIdeal F05 Fault Code
The Ideal F05 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.. It appears on 3 Ideal models in our database.
Technical description: Return Thermistor Fault
What causes the Ideal F05 fault?
This fault occurs when the boiler's control board receives an incorrect or missing signal from the sensor that measures the temperature of the water coming back from your radiators. The most common reason is that the sensor itself has developed an electrical internal failure, or the wiring connecting it to the main control board has become loose or damaged.
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 F05 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal F05 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