High
L4 on Ideal Logic Max Combi

Your boiler has sensed a problem with the internal thermometer that monitors the water temperature leaving the unit, causing it to shut down 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 Combi 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 boiler's control system receives an incorrect or missing signal from the sensor that monitors hot water leaving the unit. It is usually caused by the sensor itself failing due to age, or a loose connection in the internal wiring preventing the computer from reading the temperature accurately.

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

L1View →L2View →F2View →

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