Medium
ALL 04 on Sime Murelle HE System

Your boiler has detected a communication problem with the part that monitors the temperature of your hot water, which may cause your hot water to stop working or not reach the correct temperature.

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

D.H.W. SENSOR ALARM

Shared across the Murelle System HE 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.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like ALL 04: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

ALL 01View →ALL 05View →

All 25 fault codes on the Murelle HE System

Seeing a different code? Every code this model can display, in one place.

ALARM 01ALARM 02ALARM 03ALARM 04ALARM 05ALARM 06ALARM 07ALL 02ALL 03ALL 05ALL 06ALL 07ALL 08ALL 09ALL 10ALL 13ALL 14Flashing orange LEDLED flashing after fanOrange LED flashingOrange LED onRed LED after flow switchRed LED on (after safety stat)Red LED on (solid)

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on a combi.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →