BoilerFaultCodesThe 6 most common faults
01
ALL 02 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped below the minimum level required to operate safely.
What to try first
Locate the external filling loop (a flexible silver hose) underneath the boiler.Open the small tap or valve on the filling loop to allow cold mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.0 to 1.5 bar).Close the tap or valve tightly to stop the flow of water.
02
ALL 05 High Engineer
Your boiler has stopped working because it is unable to accurately measure the temperature of the water inside the system.
Full guide for ALL 0503
ALL 06 High Engineer
Your boiler is failing to ignite because it cannot detect the burner flame, meaning you currently have no heating or hot water.
Full guide for ALL 0604
ALL 07 High Engineer
Your boiler has detected that it has become dangerously overheated and has automatically shut itself down to prevent damage.
Full guide for ALL 0705
ALL 08 High Engineer
Your boiler has detected that the burner is not staying lit, so it has shut itself down as a safety precaution.
Full guide for ALL 0806
ALL 09 High Engineer
Your boiler has detected that water is not moving through your heating system correctly, which is preventing it from heating your home or water.
Full guide for ALL 09on the Sime Murelle Advanced HE MkII Combi
Pressure relief valveExpansion vesselPressure sensorDelivery NTC sensorWiring harnessFlame rectification electrode
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Sime shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue
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