BoilerFaultCodesIdeal F4 Or L4 Fault Code
Also written as F4ORL4 — same fault.
The Ideal F4 Or L4 fault code means: your boiler has stopped working because it is having trouble reading the temperature of the water flowing through it, so it has safely shut down to prevent overheating.. It appears on 4 Ideal models in our database.
Technical description: Flow Thermistor Fault
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 Or L4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal F4 Or 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 Logic Code Combi ESP1 manual (PDF)
- Ideal Logic Combi C24 C30 C35 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026