F 05 OR L 05 High

Ideal F 05 OR L 05 Fault Code

Also written as F05ORL05 — same fault.

The Ideal F 05 OR L 05 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.. It appears on 3 Ideal models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: RETURN THERMISTOR FAULT

What causes the Ideal F 05 OR L 05 fault?

This fault occurs when the sensor responsible for measuring the temperature of the water entering the boiler fails or sends an incorrect signal. The most common cause is the sensor itself becoming faulty or corroded, but it can also be triggered by a loose wire or a communication error within the main control board.

Typical repair cost £90-160 (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 F 05 OR L 05 fault code

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

Source

Ideal F 05 OR L 05 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