High
F 05 OR L 05 on Ideal Logic Max System

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

RETURN THERMISTOR FAULT

From this model's manual
Verified against the Ideal Logic Max System installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this 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.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F2View →L2View →F5View →L5View →

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