Common problems guide

The most common Sime Murelle HE Combi with Cylinder problems

The faults most likely to send a Sime Murelle HE Combi with Cylinder into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
9 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 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 too low.

What to try first

Locate the filling loop (usually a silver braided hose with one or two valves) underneath the boiler.Open the valve(s) slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valve(s) tightly to stop the flow of water and check the boiler display to see if the error clears.

Est. cost
£80-150
Parts
Filling loop, Pressure relief valve, Expansion vessel
Full guide for ALL 02
02
ALL 03 High DIY-safe

Your boiler has detected that the water pressure inside your heating system is too high for it to operate safely.

What to try first

Locate a radiator in your home, preferably one upstairs.Place a cloth or small container under the radiator bleed valve.Open the bleed valve slightly with a radiator key to let water out until the pressure gauge on the boiler drops to between 1 and 1.5 bar, then close the valve tightly.

Est. cost
£90-150
Parts
Pressure relief valve, Pressure sensor, Filling loop
Full guide for ALL 03
03
ALL 05 High Engineer

Your boiler has stopped working because it is unable to accurately measure the temperature of the water used for your heating system.

Est. cost
£120-220
Parts
Central heating NTC thermistor, Wiring harness
Full guide for ALL 05
04
ALL 06 High Engineer

Your boiler has detected a safety-related issue and has automatically shut down to prevent damage or dangerous operation.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for ALL 06
05
ALL 07 High Engineer

Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage or overheating.

Est. cost
£120-250
Parts
Safety thermostat, Pump, Diverter valve
Full guide for ALL 07
06
ALL 08 High Engineer

Your boiler has failed to light the burner or keep it running, so it has safely shut down to prevent unburnt gas from building up.

Est. cost
£150-300
Parts
Ignition electrode, Flame rectification probe, Gas valve
Full guide for ALL 08
Parts most often replaced

on the Sime Murelle HE Combi with Cylinder

Filling loopPressure relief valveExpansion vesselPressure sensorCentral heating NTC thermistorWiring harness

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
See the full 9-code list for the Sime Murelle HE Combi with Cylinder

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →