Medium
AL 04 on Sime Dewy 30/50 HE WM

Your boiler's hot water sensor has failed or has a bad connection, meaning the system cannot accurately monitor the temperature of the water coming out of your taps.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Domestic hot water sensor (SS) fault — combi models; check wiring connections; replace sensor if open/short circuit

Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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