High
L04 on Ideal Logic Max System

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water leaving 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

Flow Thermistor Fault

From this model's manual
Verified against the Ideal Logic Max System installation & service manual, page 75.
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 boiler's control system receives an incorrect or missing electrical signal from the sensor that monitors hot water leaving the unit. It is usually caused by the internal sensor failing due to age, or a loose connection in the wiring that prevents the boiler from safely regulating its temperature.

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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