Sime Giulia Combi 30 Fault codes & diagnostics

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

Combi Natural Gas 30 kW 2023-present
GC Number 47-283-93
Download the Sime Giulia Combi 30 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.
1 Emergency 29 High 4 Medium
Versions & GC numbers

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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
47-283-93 GIULIA COMBI 30 2023–present
Just want the most common Sime Giulia Combi 30 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 34 documented codes

Tap any card for details

02

Your boiler has stopped working because the water pressure inside the pipes has dropped too low.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath the boiler.
  2. Slowly open the one or two small valves on the hose until you hear water flowing.
  3. Watch the pressure gauge and close the valves tightly 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 02
06

Your boiler has failed to light the gas, meaning your heating and hot water will not work until the system is reset or repaired.

High DIY-safe £120-300

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Pre-payment meter users should check if they have enough credit
  3. Press and hold the 'R' reset button for 5 seconds to restart the ignition sequence

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve

Related codes

Full explanation for 06
07

Your boiler has sensed it is getting too hot and has shut itself down as a safety precaution.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Ensure there is enough pressure in the system by checking the gauge is between 1 and 1.5 bar.
  3. Try resetting the boiler by turning the selector dial to the reset position for a few seconds.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger

Related codes

Full explanation for 07
AL 02

Your boiler has detected that there is not enough water in the central heating system to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two blue or black levers) underneath the boiler.
  2. Slowly open both levers until you hear water flowing into the unit.
  3. Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close both levers tightly.
  4. If the boiler does not restart automatically, press the 'Reset' button.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for AL 02
AL 03

Your boiler has detected that there is too much water in the system, which can put unnecessary stress on the internal pipes and components.

Emergency DIY-safe £80-220

What to check first

  1. Check that the filling loop valves (usually silver flexi-hose) are tightly closed.
  2. Locate a radiator and use a bleed key to release water into a container until the pressure gauge on the boiler drops to 1.5 bar.
  3. Restart the boiler to clear the fault code.

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 sensor that monitors hot water temperature, which means you may have inconsistent or no hot water.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Temperature Sensor (NTC thermistor)
  • Wiring harness

Related codes

Full explanation for AL 04
AL 05

Your boiler has detected a problem with the internal temperature sensor that monitors the water being sent to your radiators, which means it cannot heat your home safely.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Delivery Sensor (NTC)
  • Sensor Wiring Harness

Related codes

Full explanation for AL 05
AL 06

Your boiler is failing to light the gas or cannot detect that it has lit, meaning it has shut down for safety.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching the property.
  2. Ensure your gas meter has credit if you use a prepay system.
  3. Check that the condensate pipe (the plastic pipe going outside) is not frozen during cold weather.
  4. Press the 'Reset' button on the boiler control panel.

Parts commonly replaced

  • Ignition Electrode
  • Ionisation Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 06
AL 07

Your boiler has overheated, causing a safety switch to trigger and shut down the system to prevent damage.

High DIY-safe £120-280

What to check first

  1. Allow the boiler to cool down for at least 20 minutes.
  2. Check that all radiator valves are open and that your system pressure is between 1.0 and 1.5 bar on the gauge.
  3. Press the 'Reset' button on the boiler control panel once to clear the fault code.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger (Cleaning/Descaling)

Related codes

Full explanation for AL 07
AL 08

Your boiler is struggling to detect the flame it has lit, causing it to shut down as a safety precaution.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation electrode
  • Flame sensing lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 08
Showing 11–20 of 34
AL 09

Your boiler has detected that water is not moving through the internal pipes, which prevents it from heating up safely.

High DIY-safe £180-350

What to check first

  1. Check if your radiators are turned off and ensure at least one or two are fully open.
  2. Verify that the boiler pressure gauge is between 1 and 1.5 bar.
  3. Check for any visible leaks around the pipework or radiators.

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger
  • Pump capacitor

Related codes

Full explanation for AL 09
AL 10

Your boiler has detected an issue with an internal temperature monitoring sensor, which prevents it from operating correctly for your heating or hot water.

High Engineer only £120-190

Parts commonly replaced

  • Auxiliary NTC sensor
  • Sensor wiring harness

Related codes

Full explanation for AL 10
AL 11

Your boiler is unable to control the flow of gas correctly, causing it to shut down for safety purposes.

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 is having trouble detecting the temperature of your hot water, which could mean your water isn't heating up properly.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor
  • Wiring harness

Related codes

Full explanation for AL 12
AL 13

Your boiler has shut down because it detected that the smoke and gases leaving the system have become too hot, which is a safety precautionary measure.

High Engineer only £120-280

Parts commonly replaced

  • Exhaust/Flue NTC Sensor
  • Main Heat Exchanger
  • Heat Exchanger Cleaning Kit

Related codes

Full explanation for AL 13
AL 14

Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust gases, and it has shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for AL 14
AL 15

Your boiler has stopped working because the internal computer has lost contact with the fan that clears away waste gases.

High Engineer only £100-280

Parts commonly replaced

  • Fan wiring harness
  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Full explanation for AL 15
AL 28

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

High DIY-safe £0-120

What to check first

  1. Turn the power supply to the boiler off at the fused spur switch (the wall switch).
  2. Wait for 30 seconds.
  3. Turn the power back on to clear the reset limit memory.

Parts commonly replaced

  • None (Software reset usually sufficient)
  • Spark Electrode
  • Gas Valve

Related codes

Full explanation for AL 28
AL 30

Your boiler has detected an issue with the sensor that monitors water returning from your radiators, causing the system to stop working as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor sensor
  • Sensor wiring harness
  • Main PCB

Related codes

Full explanation for AL 30
AL 37

Your boiler has detected that the electricity supply from the mains is too low for it to operate safely and has shut down to protect its components.

High DIY-safe £0-120

What to check first

  1. Check if there is a local power cut or if other appliances in your home are behaving strangely.
  2. Turn the boiler off and back on again once the power supply seems stable.
  3. If you use a pre-payment meter, ensure you have sufficient credit.

Parts commonly replaced

  • None (External power issue)
  • Printed Circuit Board (PCB) if damaged by voltage fluctuations

Related codes

Full explanation for AL 37
Showing 21–30 of 34
AL 40

Your boiler has detected an issue with the electrical power supply frequency entering the unit, preventing it from running safely.

High Engineer only £100-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Surge Protector

Related codes

Full explanation for AL 40
AL 41

Your boiler has tried and failed to stay lit six times in a row, so it has shut down for safety.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter
  2. Check if other gas appliances, like a hob, are working to confirm gas supply
  3. Reset the boiler by turning the selector dial to the 'R' position for a few seconds

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
  • PCB

Related codes

Full explanation for AL 41
AL 42

One of the buttons on your boiler's control panel has become stuck or is malfunctioning, preventing you from changing settings.

Medium DIY-safe £90-250

What to check first

  1. Carefully check each button on the control panel to see if any are physically stuck in the pushed-in position.
  2. Gently press and release each button several times to try and free them.
  3. Restart the boiler by turning the power off at the fused spur and back on again after 30 seconds.

Parts commonly replaced

  • User interface PCB
  • Control panel buttons/fascia

Related codes

Full explanation for AL 42
AL 43

Your boiler is having trouble 'speaking' to your smart thermostat or external controls, meaning it cannot receive the correct instructions to heat your home.

High Engineer only £100-250

Parts commonly replaced

  • OpenTherm Interface Cable
  • External Thermostat/Receiver
  • Boiler Main PCB

Related codes

Full explanation for AL 43
AL 44

Your boiler is failing to light because it cannot detect a steady flame within the required safety time limit.

High Engineer only £120-280

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Ionisation probe
  • PCB

Related codes

Full explanation for AL 44
AL 56

Your boiler has shut down because it is getting too hot too quickly, usually because the water isn't flowing through the system fast enough.

High DIY-safe £100-300

What to check first

  1. Check that all radiator valves are fully open
  2. Check the boiler pressure gauge and top up to 1.5 bar if low
  3. Ensure there is no air trapped in the radiators by bleeding them
  4. Reset the boiler using the control knob

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger (de-scaling)
  • Thermistor (NTC sensor)

Related codes

Full explanation for AL 56
AL 57

Your boiler has detected an issue with the water flow temperature, possibly due to trapped air or a circulation problem, and has locked itself to prevent damage.

High DIY-safe £100-250

What to check first

  1. Check that your radiator valves are fully open
  2. Bleed your radiators to remove any trapped air
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it is low
  4. Press the Reset button on the control panel

Parts commonly replaced

  • Flow temperature thermistor (NTC sensor)
  • Circulation pump
  • Automatic air vent

Related codes

Full explanation for AL 57
AL 72

Your boiler has detected that a temperature sensor is not attached correctly or is sending an unusual reading, causing the system to stop working for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Sensor retaining clip
  • Wiring harness

Related codes

Full explanation for AL 72
AL 80

Your boiler has detected an internal communication failure between the control board and the gas valve, meaning the system cannot safely manage the flow of gas to start the burner.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve wiring loom
  • Gas valve
  • Main PCB

Related codes

Full explanation for AL 80
AL 95

Your boiler is struggling to maintain a steady flame, causing the system to cut out for safety reasons.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for AL 95
Showing 31–34 of 34
AL 98

Your boiler's internal computer has encountered a startup error and cannot communicate properly to begin the heating process.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Low voltage wiring harness

Related codes

Full explanation for AL 98
AL 99

Your boiler's internal computer has encountered a critical failure and can no longer communicate with the rest of the system.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Loom

Related codes

Full explanation for AL 99
ALL 04

Your boiler has lost the ability to measure the temperature of your hot water, which usually means it cannot provide hot water to your taps.

Medium Engineer only £100-£180

Parts commonly replaced

  • DHW NTC Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for ALL 04
ALL 09

Your boiler has lost the ability to monitor its own water pressure, meaning it has shut down as a safety precaution.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure transducer
  • Wiring harness
  • Main PCB

Related codes

Full explanation for ALL 09
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