Sime Meridian HE Fault codes & diagnostics

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

Combi Natural Gas 2013-2018 Discontinued
GC Numbers 47-283-4447-283-45
Download the Sime Meridian HE manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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9 High
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-283-44 Meridian HE 25 2013–2018
47-283-45 Meridian HE 30 2013–2018
Just want the most common Sime Meridian HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 9 documented codes

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AL 02

Your boiler has stopped working because the water pressure is too low and needs to be topped up.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (the silver braided hose) underneath the boiler.
  2. Slowly open the small tap(s) on the filling loop until you hear water entering the system.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.2 bar, then close the tap(s) fully.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for AL 02
AL 05

Your boiler has detected a fault with the main temperature sensor that monitors the water leaving the unit, preventing it from heating up correctly.

High Engineer only £90-160

Parts commonly replaced

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

Related codes

Full explanation for AL 05
AL 06

Your boiler is failing to light or stay lit because it cannot detect a flame.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm your gas supply is on
  2. Ensure your gas meter has credit if you use a prepay meter
  3. Try resetting the boiler by turning the selector switch to the 'R' position for a few seconds

Parts commonly replaced

  • Ignition electrode
  • Detection electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 06
AL 07

Your boiler has overheated, prompting a safety device to shut it down to prevent damage.

High DIY-safe £90-180

What to check first

  1. Check that all radiator valves are fully open
  2. Check the system pressure is between 1.0 and 1.5 bar
  3. Bleed any trapped air from your radiators
  4. Attempt to reset the boiler using the selector switch

Parts commonly replaced

  • Safety Thermostat (Limit Statutory)
  • System Pump
  • Overheat Sensor

Related codes

Full explanation for AL 07
AL 08

Your boiler is struggling to detect a flame, which means it cannot stay lit to provide heating or hot water.

High DIY-safe £90-180

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Verify if other gas appliances in your home, such as a hob, are working correctly
  3. Press the reset button on the boiler control panel

Parts commonly replaced

  • Ignition electrode
  • Ionisation probe
  • Gas valve

Related codes

Full explanation for AL 08
AL 10

Your boiler's computer is confused about how the internal pipework is set up because an optional secondary sensor is missing or malfunctioning.

High Engineer only £90-180

Parts commonly replaced

  • Auxiliary NTC Sensor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for AL 10
AL 13

Your boiler has detected that the exhaust gases are too hot or the sensor monitoring them is broken, so it has shut down for safety.

High Engineer only £120-£220

Parts commonly replaced

  • Exhaust sensor (flue probe)
  • Main PCB

Related codes

Full explanation for AL 13
AL 14

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

High Engineer only £120-220

Parts commonly replaced

  • Exhaust sensor (smoke probe)
  • Wiring harness

Related codes

Full explanation for AL 14
AL 15

Your boiler has detected a communication problem with the fan, which means it cannot safely clear exhaust fumes and will not start.

High Engineer only £120-300

Parts commonly replaced

  • Fan wiring harness
  • Fan motor
  • Main PCB

Related codes

Full explanation for AL 15