BoilerFaultCodesIdeal L4 Fault Code
The Ideal L4 fault code means: your boiler has detected a problem with the internal sensor that monitors the temperature of the water as it leaves the unit, causing the system to shut down as a safety precaution.. It appears on 17 Ideal models in our database.
Technical description: Flow Thermistor Fault
What causes the Ideal L4 fault?
This fault occurs when the boiler's control board can no longer get an accurate reading from the sensor that monitors hot water temperature. The most common reason is that the sensor has physically failed or developed an electrical short, though loose or damaged wiring between the sensor and the main board can also cause the connection to drop out.
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 L4 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atlantic Combi Repair: £120-220
- EXCLUSIVE2 Repair: £100-£180
- GB24 / GB30 Repair: £120-220
- i Combi 2 Repair: £100-£220
- INDEPENDENT + COMBI Repair: £100-£180
- Independent C24 Repair: £120-250
- INDEPENDENT SYSTEM Repair: £100-£220
- Independent System S15 Repair: £100-£220
- INSTINCT2 Repair: £100-£180
- Logic Code Combi ESP1 Repair: £100-£180
- Logic Combi C24 C30 C35 Repair: £90-160
- Logic Combi ESP1 Repair: £90-160
- LOGIC HEAT Repair: £100-£220
- Logic Max Heat Repair: £100-£220
- Logic Max System Repair: £100-£180
- LOGIC SYSTEM Repair: £100-£220
- Logic+ Heat H Repair: £90-160
Source
Ideal L4 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
- Ideal GB24 / GB30 manual (PDF)
- Ideal Independent System S15 manual (PDF)
- Ideal Logic+ Heat H manual →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026