BoilerFaultCodes 06
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Sime Brava One HE Fault codes & diagnostics
48 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural Gas 2016-present
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Severity at a glance
Each cell = one fault code. Hover to identify. 3 Emergency
40 High
2 Medium
3 Unrated
Just want the most common Sime Brava One HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 48 documented codes
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AL 00
Τελευταία δυσλειτουργία/βλάβη που έχει παρουσιαστεί
AL 01 Your boiler has shut down because it detected that exhaust gases are not escaping correctly through the flue, which is a safety risk.
Your boiler has shut down because it detected that exhaust gases are not escaping correctly through the flue, which is a safety risk.
Parts commonly replaced
- Flue gas thermostat
- Flue seals
- Heat exchanger
Related codes
AL 02 Your boiler has stopped working because the water pressure is too low and needs to be topped up.
Your boiler has stopped working because the water pressure is too low and needs to be topped up.
What to check first
- Locate the flexible silver filling loop under or near the boiler.
- Slowly open the one or two small taps on the loop until you hear water entering.
- Watch the pressure gauge and close the taps firmly once the needle reaches between 1.0 and 1.2 bar.
Parts commonly replaced
- Filling loop
- Pressure sensor
- Expansion vessel
Related codes
AL 03 Your boiler has detected that the water pressure is too high, which can cause the system to stop working to prevent damage.
Your boiler has detected that the water pressure is too high, which can cause the system to stop working to prevent damage.
What to check first
- Locate a radiator bleed valve and use a key to release water into a container until the pressure gauge on the boiler drops.
- Ensure the filling loop (the silver braided hose under the boiler) is tightly closed and not accidentally left open.
- Monitor the pressure gauge until it reaches approximately 1.2 bar, then close the bleed valve.
Parts commonly replaced
- Filling loop valve
- Pressure sensor
- Expansion vessel
Related codes
AL 04 Your boiler has detected a problem with the temperature sensor that controls your hot water, meaning you may experience cold or inconsistently heated water.
Your boiler has detected a problem with the temperature sensor that controls your hot water, meaning you may experience cold or inconsistently heated water.
Parts commonly replaced
- Domestic Hot Water (DHW) NTC Sensor
- Sensor wiring harness
Related codes
AL 05 Your boiler has detected a fault with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot operate safely or effectively.
Your boiler has detected a fault with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot operate safely or effectively.
Parts commonly replaced
- Flow NTC temperature sensor
- Wiring harness
Related codes
AL 06 Your boiler is failing to light properly, which means you currently have no heating or hot water.
Your boiler is failing to light properly, which means you currently have no heating or hot water.
What to check first
- Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.
- Verify that your gas meter has credit and the isolation valve is open.
- Press and hold the 'Reset' button for 3 seconds to attempt a restart.
Parts commonly replaced
- Ignition Electrode
- Flame Sensing Electrode
- Gas Valve
Related codes
AL 07 Your boiler has switched itself off to prevent overheating, usually because the water isn't moving through the system correctly or there is trapped air.
Your boiler has switched itself off to prevent overheating, usually because the water isn't moving through the system correctly or there is trapped air.
What to check first
- Check that your radiator valves and isolation valves under the boiler are fully open.
- Bleed all radiators to remove any trapped air that might be causing a blockage.
- Attempt to reset the boiler by turning the selector knob to the 'R' position for a few seconds.
Parts commonly replaced
- Safety Thermostat (Limitswitch)
- Central Heating Pump
- Overheat Sensor
Related codes
AL 08 Your boiler is struggling to detect a flame, which means it cannot stay lit to provide heating or hot water.
Your boiler is struggling to detect a flame, which means it cannot stay lit to provide heating or hot water.
What to check first
- Check if other gas appliances (like a hob) are working to confirm your gas supply is active.
- If you have a prepayment meter, check that you have sufficient credit.
- Try to reset the boiler by turning the selector switch to the reset position for a few seconds.
Parts commonly replaced
- Ignition electrode
- Flame sensing electrode
- Gas valve
- PCB
Related codes
Showing 11–20 of 48
AL 09 Your boiler has stopped working because water is not moving around the system correctly, which could be due to a blockage or a stuck pump.
Your boiler has stopped working because water is not moving around the system correctly, which could be due to a blockage or a stuck pump.
What to check first
- Check that your system pressure is between 1 and 1.5 bar on the pressure gauge
- Ensure all radiator valves and isolation valves under the boiler are fully open
- Try bleeding your radiators to remove any trapped air that might be blocking flow
Parts commonly replaced
- Circulation Pump
- Central Heating Filter
- Pump Impeller
Related codes
AL 10 Your boiler has stopped working because its internal computer is confused about its settings or a sensor has developed an electrical fault.
Your boiler has stopped working because its internal computer is confused about its settings or a sensor has developed an electrical fault.
Parts commonly replaced
- Auxiliary temperature sensor
- Wiring harness
- Printed Circuit Board (PCB)
Related codes
AL 11 Your boiler has detected a communication error with the component that controls the gas supply, preventng it from firing up safely.
Your boiler has detected a communication error with the component that controls the gas supply, preventng it from firing up safely.
Parts commonly replaced
- Gas Valve
- Wiring Harness
- Printed Circuit Board (PCB)
Related codes
AL 12 Your boiler's computer has been set to the wrong internal configuration, causing it to shut down for safety because it doesn't recognize how it is built.
Your boiler's computer has been set to the wrong internal configuration, causing it to shut down for safety because it doesn't recognize how it is built.
Parts commonly replaced
- Main PCB (Print Circuit Board)
Related codes
AL 13 Your boiler has shut down because it detected that the exhaust gases are getting too hot or the sensor that monitors them has failed.
Your boiler has shut down because it detected that the exhaust gases are getting too hot or the sensor that monitors them has failed.
Parts commonly replaced
- Smoke probe (Exhaust sensor)
- Main PCB
Related codes
AL 14 Your boiler has detected an issue with the sensor that monitors exhaust gases, meaning it has shut down as a safety precaution.
Your boiler has detected an issue with the sensor that monitors exhaust gases, meaning it has shut down as a safety precaution.
Parts commonly replaced
- Flue gas NTC sensor (smoke probe)
- Wiring harness
Related codes
AL 15 Your boiler has detected a communication problem with its internal fan, which is preventing it from starting up safely for heating and hot water.
Your boiler has detected a communication problem with its internal fan, which is preventing it from starting up safely for heating and hot water.
Parts commonly replaced
- Fan wiring harness
- Main PCB
- Fan motor
Related codes
AL 18 Your boiler has detected that the water drain for condensation is backed up or blocked, which has caused the system to shut down for safety.
Your boiler has detected that the water drain for condensation is backed up or blocked, which has caused the system to shut down for safety.
What to check first
- Check the external plastic 'condensate' pipe for signs of being frozen if the weather is cold.
- Thaw any frozen external pipes using a hot water bottle or a jug of warm (not boiling) water.
- Ensure the plastic pipe end is not submerged in water or blocked by debris/leaves.
Parts commonly replaced
- Condensate siphon
- Condensate discharge pipework
- Water level electrode
Related codes
AL 28 Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety reasons.
Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety reasons.
What to check first
- Wait for 60 minutes without touching the boiler to allow the safety timer to expire.
- Verify that the gas supply to the property is active and other gas appliances are working.
- Attempt one final reset using the selector dial once the 'AL 28' code clears.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
AL 30 Your boiler has detected a problem with the sensor that monitors water temperature returning from your radiators, and it has stopped working for safety.
Your boiler has detected a problem with the sensor that monitors water temperature returning from your radiators, and it has stopped working for safety.
Parts commonly replaced
- Return NTC temperature sensor
- Connection wiring
Related codes
Showing 21–30 of 48
AL 37 Your boiler has stopped working because the electricity supply coming into your home is currently too weak or unstable to power the unit safely.
Your boiler has stopped working because the electricity supply coming into your home is currently too weak or unstable to power the unit safely.
Parts commonly replaced
- No parts usually required
- Printed Circuit Board (PCB) if damaged by surges
Related codes
AL 40 Your boiler has detected an issue with the electrical power supply coming into your home, meaning the frequency of the electricity does not match what the boiler needs to operate safely.
Your boiler has detected an issue with the electrical power supply coming into your home, meaning the frequency of the electricity does not match what the boiler needs to operate safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Surge Protector
Related codes
AL 41 Your boiler has failed to stay lit after six attempts and has shut down to prevent damage, possibly due to a fuel supply issue or a faulty internal sensor.
Your boiler has failed to stay lit after six attempts and has shut down to prevent damage, possibly due to a fuel supply issue or a faulty internal sensor.
What to check first
- Check if other gas appliances (like a hob) are working to confirm your gas supply is active.
- If you have a prepay meter, check that you have sufficient credit.
- Press and hold the 'Reset' button for 1 to 5 seconds to attempt a restart.
Parts commonly replaced
- Ignition electrode
- Detection electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
AL 42 Your boiler's controls have detected a stuck or malfunctioning button on the front panel, preventing it from processing your commands.
Your boiler's controls have detected a stuck or malfunctioning button on the front panel, preventing it from processing your commands.
What to check first
- Carefully press and release each button on the control panel to see if any are physically stuck or depressed.
- Gently wipe the control panel with a dry, lint-free cloth to ensure no debris is jamming the buttons.
- Turn the electrical power to the boiler off and back on again to reset the electronic board.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Control Interface/Bezel
Related codes
AL 43 Your boiler is struggling to talk to your smart thermostat or wall controller, preventing the system from following your heating instructions.
Your boiler is struggling to talk to your smart thermostat or wall controller, preventing the system from following your heating instructions.
What to check first
- Check that your wall-mounted thermostat or remote control has power or fresh batteries
- Ensure the thermostat is properly clicked into its wall bracket
- Briefly turn the power to the boiler off and back on to reset the communication link
Parts commonly replaced
- OpenTherm Bridge/Receiver
- Wall Controller
- Low voltage wiring
Related codes
AL 44 Your boiler is failing to light because its internal computer and gas valve are not communicating correctly.
Your boiler is failing to light because its internal computer and gas valve are not communicating correctly.
Parts commonly replaced
- Main PCB (Electronic Board)
- Gas Valve
Related codes
AL 56 Your boiler has shut down because the water is not flowing through the system quickly enough, causing the temperature difference between the pipes to become too large.
Your boiler has shut down because the water is not flowing through the system quickly enough, causing the temperature difference between the pipes to become too large.
What to check first
- Check that at least two or three radiator valves are fully open to allow water flow.
- Ensure the central heating system pressure is between 1.0 and 1.5 bar on the gauge.
- Check if any bypass valves are closed and try resetting the boiler once.
- Ensure there are no air locks by bleeding your radiators.
Parts commonly replaced
- Circulation Pump
- Main Heat Exchanger
- Temperature Sensors (NTC)
- System Filter
Related codes
AL 57 Your boiler has temporarily locked itself because it has detected an unusual temperature reading and needs to recalibrate its internal sensors to work correctly again.
Your boiler has temporarily locked itself because it has detected an unusual temperature reading and needs to recalibrate its internal sensors to work correctly again.
What to check first
- Locate the selector dial on the front of the boiler control panel.
- Turn the dial to the 'OFF/RESET' position and wait for 30 seconds.
- Turn the dial back to the desired setting to trigger the automatic self-calibration process.
Parts commonly replaced
- None (Software reset usually resolves)
- Flow Temperature Sensor (NTC)
- Main PCB
Related codes
AL 72 Your boiler has detected that a temperature sensor is not sitting correctly on its pipe, preventing the system from accurately monitoring the heat of your water.
Your boiler has detected that a temperature sensor is not sitting correctly on its pipe, preventing the system from accurately monitoring the heat of your water.
Parts commonly replaced
- Delivery temperature sensor (NTC)
- Sensor retaining clip
Related codes
AL 74 Your boiler has detected an issue with a temperature sensor that monitors the water being sent to your taps or radiators, meaning it cannot accurately gauge the water heat.
Your boiler has detected an issue with a temperature sensor that monitors the water being sent to your taps or radiators, meaning it cannot accurately gauge the water heat.
Parts commonly replaced
- Delivery NTC Sensor
- Sensor Wiring Harness
Related codes
Showing 31–40 of 48
AL 77 Your boiler has detected an electrical issue with the internal gas valve, which is preventing it from lighting the burner safely.
Your boiler has detected an electrical issue with the internal gas valve, which is preventing it from lighting the burner safely.
Parts commonly replaced
- Gas Valve
- Main PCB (Printed Circuit Board)
- Wiring Harness
Related codes
AL 78 Your boiler has detected an internal electrical fault with the gas control valve, preventing it from firing safely.
Your boiler has detected an internal electrical fault with the gas control valve, preventing it from firing safely.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
AL 79 Your boiler has detected an internal electrical fault with the gas control valve or the main control board, preventing it from firing up safely.
Your boiler has detected an internal electrical fault with the gas control valve or the main control board, preventing it from firing up safely.
Parts commonly replaced
- Gas valve
- PCB (Main Circuit Board)
- Wiring harness
Related codes
AL 80 Your boiler has detected an internal communication failure between the main control board and the gas valve, meaning it cannot safely manage the fuel supply.
Your boiler has detected an internal communication failure between the main control board and the gas valve, meaning it cannot safely manage the fuel supply.
Parts commonly replaced
- Gas Valve
- Wiring Loom
- Main PCB
Related codes
AL 81 Your boiler has detected an issue with the air or gas mixture during ignition, often caused by a blocked vent or a sensor problem, and has locked itself out for safety.
Your boiler has detected an issue with the air or gas mixture during ignition, often caused by a blocked vent or a sensor problem, and has locked itself out for safety.
Parts commonly replaced
- Air pressure switch
- Ignition electrode
- Gas valve
- Flue seals
Related codes
AL 82 Your boiler has shut down because it has struggled to start or maintain a steady flame several times in a row.
Your boiler has shut down because it has struggled to start or maintain a steady flame several times in a row.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Detection probe
Related codes
AL 83 Your boiler is struggling to burn gas correctly, often because of air in the pipes or a blockage in the chimney.
Your boiler is struggling to burn gas correctly, often because of air in the pipes or a blockage in the chimney.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Flue seals
Related codes
AL 84 Your boiler has detected that the gas supply pressure coming into the unit is too low to operate correctly.
Your boiler has detected that the gas supply pressure coming into the unit is too low to operate correctly.
Parts commonly replaced
- Gas Valve
- Gas Meter Regulator
- External Gas Pipework
Related codes
AL 88 Your boiler's internal computer has detected a serious electronic failure and has shut down to protect its circuits.
Your boiler's internal computer has detected a serious electronic failure and has shut down to protect its circuits.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
Related codes
AL 89 Your boiler is struggling to maintain a steady flame and has shut down as a safety precaution to ensure gas is burning correctly.
Your boiler is struggling to maintain a steady flame and has shut down as a safety precaution to ensure gas is burning correctly.
Parts commonly replaced
- Ignition/Ionisation Electrode
- Gas Valve
- Air Pressure Diaphragm
Related codes
Showing 41–48 of 48
AL 90 Your boiler is struggling to manage the correct balance of gas and air needed for a safe flame, causing it to shut down for safety.
Your boiler is struggling to manage the correct balance of gas and air needed for a safe flame, causing it to shut down for safety.
Parts commonly replaced
- Ignition/Ionisation electrode
- Air pressure switch
- Gas Valve
- Venting diaphragm
Related codes
AL 92 Your boiler's internal sensor has detected an issue with the air and gas mixture, causing the system to stop for safety.
Your boiler's internal sensor has detected an issue with the air and gas mixture, causing the system to stop for safety.
Parts commonly replaced
- Ignition/Sensing Electrode
- Air Pressure Switch Diaphragm
- Venturi Tube
Related codes
AL 93 Your boiler is struggling to burn gas correctly and is failing to reach its required performance levels, causing the system to shut down for safety.
Your boiler is struggling to burn gas correctly and is failing to reach its required performance levels, causing the system to shut down for safety.
Parts commonly replaced
- Gas valve
- Electrode
- Fan
- Control board
Related codes
AL 95 Your boiler is struggling to maintain a steady flame, causing it to shut down to prevent damage or unsafe operation.
Your boiler is struggling to maintain a steady flame, causing it to shut down to prevent damage or unsafe operation.
Parts commonly replaced
- Ionisation electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
AL 96 Your boiler has shut down because it cannot safely expel exhaust fumes, meaning the vent to the outside may be blocked.
Your boiler has shut down because it cannot safely expel exhaust fumes, meaning the vent to the outside may be blocked.
Parts commonly replaced
- Flue terminal
- Air pressure switch
- Flue seals
- Fan
Related codes
AL 98 Your boiler's internal computer has encountered a software glitch while trying to start up.
Your boiler's internal computer has encountered a software glitch while trying to start up.
What to check first
- Press and hold the 'R' (Reset) button for a few seconds.
- Turn the boiler power off at the main fused spur switch, wait 30 seconds, and turn it back on.
- If the code persists after a reset, you will need to call a Gas Safe engineer.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
Related codes
AL 99 Your boiler's internal computer has suffered a total failure and can no longer control the heating system.
Your boiler's internal computer has suffered a total failure and can no longer control the heating system.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
Related codes
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Status & diagnostic codes 1 operating states & engineer diagnostics
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1 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
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