How much does it cost to fix Ideal error code L4 or F4?

Typical repair cost for the Ideal L4 or F4 fault is £120-£250 including labour.

L4 or F4 High

Ideal L4 or F4 Fault Code

Q: What does the Ideal L4 or F4 fault code mean?

Your boiler has detected that water is either not moving through the system properly or a temperature sensor is giving a faulty reading, causing the unit to shut down for safety.

Also written as L4ORF4 — same fault.

The Ideal L4 or F4 fault code means: your boiler has detected that water is either not moving through the system properly or a temperature sensor is giving a faulty reading, causing the unit to shut down for safety.. It appears on 8 Ideal models in our database.

Technical description: Control / no flow thermistor fault

Typical repair cost £120-£250 (including labour)

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 or F4 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ideal L4 or 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 27 April 2026