BoilerFaultCodesIdeal F4 Fault Code
The Ideal F4 fault code means: your boiler has detected an issue with the sensor that measures the temperature of the water leaving the unit, preventing it from heating your home safely.. It appears on 13 Ideal models in our database.
Technical description: Flow Thermistor Fault
What causes the Ideal F4 fault?
This fault occurs when the internal sensor responsible for monitoring the heat of the water leaving the boiler fails to send a clear signal back to the control board. The most common reason is that the sensor has physically degraded or developed an electrical short, meaning the boiler can no longer safely tell if the water is getting too hot. In some cases, loose wiring or a connection issue between the sensor and the main computer can also trigger this shutdown.
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 F4 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atlantic Combi Repair: £120-220
- Concorde Repair: £90-160
- GB24 / GB30 Repair: £120-200
- i Combi 2 Repair: £100-£220
- Instinct2 24 Repair: £90-160
- Logic Air Repair: £150-300
- Logic Code Combi ESP1 Repair: £90-180
- Logic Combi C24 C30 C35 Repair: £90-£160
- Logic Combi ESP1 Repair: £90-£160
- Logic Max Combi Repair: £90-180
- Logic+ Heat H Repair: £90-160
- Logic+ System Repair: £120-220
- Mexico Repair: £120-£200
Source
Ideal F4 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