Sime Murelle One HE Fault codes & diagnostics

29 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 2019-present
GC Numbers 47-283-7947-283-89
Download the Sime Murelle One HE manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
3 Emergency 25 High 1 Medium
Just want the most common Sime Murelle One HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 29 documented codes

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02

Your boiler has stopped because the water pressure inside the heating system has dropped too low to operate safely.

High DIY-safe £80-120

What to check first

  1. Locate the external filling loop, which is a silver braided hose connected between two pipes near your boiler.
  2. Open the valves at both ends of the hose to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves tightly and remove the filling loop if required by your specific setup.

Parts commonly replaced

  • Pressure relief valve
  • Pressure gauge
  • Filling loop

Related codes

Full explanation for 02
06

Your boiler has attempted to light the gas burner several times but has failed to detect a flame, causing it to shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 06
07

Your boiler has detected that it is overheating and has automatically switched itself off to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Safety thermostat
  • Central heating pump
  • System filter

Related codes

Full explanation for 07
AL 01

Your boiler has shut down because the exhaust gases have reached an unsafe temperature, triggered by a safety sensor in the flue system.

Emergency Engineer only £120-250

Parts commonly replaced

  • Smoke thermostat (flue gas probe)
  • Heat exchanger cleaning
  • Flue seals

Related codes

Full explanation for AL 01
AL 02

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose with small valves) underneath the boiler.
  2. Slowly open both valves to allow water into the system while watching the pressure gauge.
  3. Close both valves firmly once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for AL 02
AL 03

Your boiler has detected that the water pressure is too high, which can cause the system to stop working to protect itself.

Emergency DIY-safe £0-120

What to check first

  1. Locate the radiator bleed valve on a convenient radiator.
  2. Using a radiator key and a cloth, slowly open the valve to release a small amount of water into a container.
  3. Monitor the boiler pressure gauge until it drops to between 1.0 and 1.5 bar, then tighten the valve.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for AL 03
AL 04

Your boiler has detected a problem with the temperature sensor that manages your hot water, which usually means your taps will only run cold.

High Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Sensor
  • Sensor wiring harness

Related codes

Full explanation for AL 04
AL 05

Your boiler has detected a fault with the internal temperature sensor that monitors water leaving the unit, causing the system to shut down as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Sensor wiring harness

Related codes

Full explanation for AL 05
AL 06

Your boiler has failed to light the flame, which means it cannot provide you with any heating or hot water at the moment.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching the property.
  2. Verify that your gas meter has credit if you use a pre-payment meter.
  3. Ensure the gas stopcock (yellow valve) is in the open position.
  4. Press the 'Reset' button on the boiler control panel once to see if it clears the fault.

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve
  • PCB (Printed Circuit Board)

Related codes

Full explanation for AL 06
AL 07

Your boiler has switched itself off because it has detected that the internal water temperature has become too hot.

High DIY-safe £100-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system water pressure is between 1 and 1.5 bar on the pressure gauge
  3. Press and hold the 'R' (Reset) button for a few seconds to restart the boiler
  4. Bleed any air from your radiators

Parts commonly replaced

  • Overheat Thermostat
  • System Pump
  • Main Heat Exchanger (Cleaning/Flushing)

Related codes

Full explanation for AL 07
Showing 11–20 of 29
AL 08

Your boiler is struggling to burn the gas cleanly, so it has temporarily shut down as a safety precaution to protect itself.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flue seal

Related codes

Full explanation for AL 08
AL 09

Your boiler has stopped working because water isn't moving through the system as it should, often due to a pump issue or a blockage.

High DIY-safe £180-350

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the gauge
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Restart the boiler using the reset button to see if the pump clears itself

Parts commonly replaced

  • Circulation pump
  • Central heating filter
  • Pump impeller

Related codes

Full explanation for AL 09
AL 10

Your boiler has detected an internal communication error with its sensors or settings, meaning it cannot accurately manage the heating system.

High Engineer only £90-180

Parts commonly replaced

  • Auxiliary Temperature Sensor
  • Wiring Loom
  • Main PCB

Related codes

Full explanation for AL 10
AL 11

Your boiler has lost its electronic connection to the part that controls the gas flow, meaning it cannot safely stay lit to provide heating or hot water.

High Engineer only £120-£350

Parts commonly replaced

  • Gas Valve Modulator Coil
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for AL 11
AL 12

Your boiler's computer has been set to the wrong internal configuration, meaning it doesn't know if it is an open or sealed system.

High Engineer only £80-120

Parts commonly replaced

  • None (Software adjustment required)
  • Printed Circuit Board (PCB) if settings won't save

Related codes

Full explanation for AL 12
AL 13

Your boiler has shut down because a temperature sensor in the flue has detected that the exhaust gases are getting too hot.

High Engineer only £120-220

Parts commonly replaced

  • Smoke probe (Exhaust sensor)
  • Main heat exchanger cleaning

Related codes

Full explanation for AL 13
AL 14

Your boiler has detected a problem with the sensor that monitors exhaust fumes, causing the system to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flue gas sensor (Smoke probe)
  • Wiring harness

Related codes

Full explanation for AL 14
AL 15

Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not communicating correctly with the main control board.

High Engineer only £120-£350

Parts commonly replaced

  • Fan wiring harness
  • Extraction fan
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 15
AL 18

Your boiler has stopped working because the internal pipe that drains away waste water is likely blocked or full.

High DIY-safe £80-160

What to check first

  1. Locate the external plastic pipe leading from the boiler and check if the end is frozen or blocked by debris.
  2. Carefully pour warm (not boiling) water over any frozen sections of the external pipe.
  3. Reset the boiler by turning the selector dial to the 'R' position for a few seconds.

Parts commonly replaced

  • Condensate siphon
  • Condensate electrode/sensor
  • External pipe insulation

Related codes

Full explanation for AL 18
AL 28

Your boiler has been reset too many times in a short period and has now locked itself for one hour as a safety precaution.

High Engineer only £100-350

What to check first

  1. Wait for 60 minutes without touching the boiler to allow the lockout timer to expire
  2. Once the hour has passed, attempt one final reset
  3. If the boiler locks out again, do not attempt further resets and call a Gas Safe engineer

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 28
Showing 21–29 of 29
AL 37

Your boiler has stopped working because the electrical power coming into your home has dropped to a level that is too low for the system to run safely.

High Engineer only £0-120

Parts commonly replaced

  • None - External power issue
  • PCB (if damaged by voltage drop)

Related codes

Full explanation for AL 37
AL 40

Your boiler has detected an issue with the electrical power supply frequency coming into your home, which is preventing it from running safely.

High Engineer only £100-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Voltage Protector

Related codes

Full explanation for AL 40
AL 41

Your boiler has failed to keep its flame lit six times in a row and has shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Verify that other gas appliances in the home are working correctly
  3. Reset the boiler by turning the selector switch to the reset position for a few seconds

Parts commonly replaced

  • Ignition and detection electrode
  • Gas valve
  • Spark generator

Related codes

Full explanation for AL 41
AL 42

Your boiler has detected that one of the buttons on the control panel is stuck or faulty, which is preventing the system from operating correctly.

Medium DIY-safe £120-300

What to check first

  1. Check all buttons on the front panel to see if any are physically stuck in the 'pressed' position.
  2. Gently press and release every button several times to ensure they move freely.
  3. Restart the boiler using the reset button to see if the error clears.

Parts commonly replaced

  • Control Panel Interface
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 42
AL 43

Your boiler has lost its connection to your smart thermostat or remote control system, meaning they can no longer talk to each other to manage your heating.

High DIY-safe £80-180

What to check first

  1. Check that your wall thermostat is powered on and has fresh batteries if applicable.
  2. Ensure any wireless receiver boxes plugged into or near the boiler have power lights on.
  3. Try resetting the boiler by turning the selector switch to the 'R' position for a few seconds.

Parts commonly replaced

  • OpenTherm Bridge/Interface
  • Room Thermostat
  • Wiring Connection

Related codes

Full explanation for AL 43
AL 72

Your boiler has detected that a temperature sensor is not measuring the heat of the water correctly, likely because it has come loose or is faulty.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Delivery Sensor (NTC)
  • Sensor retaining clip

Related codes

Full explanation for AL 72
AL 81

Your boiler has detected a problem with how the gas is burning when it tries to start, likely caused by a blockage in the air or exhaust pipes.

High Engineer only £120-£350

Parts commonly replaced

  • Air pressure switch
  • Gas valve
  • Flue seals
  • Burner electrode

Related codes

Full explanation for AL 81
AL 83

Your boiler is having trouble burning gas correctly, which is likely caused by air in the pipes or a dirty internal sensor.

High Engineer only £90-250

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve

Related codes

Full explanation for AL 83
AL 96

Your boiler has shut down because it cannot safely expel waste gases through the exhaust pipe, often due to an external blockage or a buildup of debris.

Emergency Engineer only £100-250

Parts commonly replaced

  • Flue seals
  • Pressure switch
  • Fan assembly
  • Flue terminal

Related codes

Full explanation for AL 96
Status & diagnostic codes

1 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

AL 62 Diagnostic Your boiler has lost its fine-tuned settings and needs to run a setup process to ensure it is burning gas safely and efficiently.
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