BoilerFaultCodesIdeal L5 or F5 Fault Code
Also written as L5ORF5 — same fault.
The Ideal L5 or F5 fault code means: your boiler has lost the ability to accurately measure the temperature of the water returning to it, so it has shut down as a precaution to prevent overheating.. It appears on 12 Ideal models in our database.
Technical description: RETURN THERMISTOR FAULT
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like L5 or F5: no call-out fees, no surprise bills.
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Ideal models that show the L5 or F5 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atlantic Combi Repair: £120-220
- CLASSIC2 Repair: £120-190
- ESPRIT ECO2 Repair: £120-190
- EXCLUSIVE2 Repair: £120-190
- i-mini C24 / C30 Repair: £120-£220
- INDEPENDENT + COMBI Repair: £120-190
- Independent C24 Repair: £120-190
- INSTINCT2 Repair: £120-190
- Instinct2 24 Repair: £120-190
- Logic Code Combi ESP1 Repair: £120-200
- Logic Combi C24 C30 C35 Repair: £120-200
- Logic Combi ESP1 Repair: £120-220
Source
Ideal L5 or F5 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 31 August 2026