BoilerFaultCodes 05
Your boiler is simply performing a routine automatic safety check to prevent its internal parts from freezing up during cold weather.
Ariston Euro Combi 30 MFFI Fault codes & diagnostics
62 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural Gas 30 kW Discontinued
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Severity at a glance
Each cell = one fault code. Hover to identify. 1 Emergency
47 High
8 Medium
6 Low
Just want the most common Ariston Euro Combi 30 MFFI faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 62 documented codes
Tap any card for details
06 Your boiler is currently running its built-in protection system to prevent the internal pipes from freezing due to cold weather.
Your boiler is currently running its built-in protection system to prevent the internal pipes from freezing due to cold weather.
Parts commonly replaced
- NTC Temperature Sensor
- PCB
10 Your boiler has failed to ignite or stay lit because it cannot detect a gas supply or a flame signal.
Your boiler has failed to ignite or stay lit because it cannot detect a gas supply or a flame signal.
What to check first
- Check that your gas meter has credit (if on a prepayment meter)
- Check that other gas appliances, like a cooker, are working to confirm gas supply
- Press the 'Reset' button on the boiler control panel once
- Ensure the gas stop tap (gas cock) is fully open
Parts commonly replaced
- Detection Electrode
- Ignition Electrode
- Gas Valve
12 Your boiler is struggling to heat your tap water effectively, meaning it may not reach the desired temperature or the flow is too weak.
Your boiler is struggling to heat your tap water effectively, meaning it may not reach the desired temperature or the flow is too weak.
What to check first
- Check that the cold water mains stopcock is fully open
- Inspect all hot water taps for limescale buildup and clean the aerators
- Ensure the temperature control dial on the front of the boiler is set correctly
Parts commonly replaced
- DHW Temperature Sensor (NTC)
- Domestic Hot Water Plate Heat Exchanger
Related codes
13 Your boiler has detected an internal communication error or a logic failure within the main control system, meaning it cannot verify if it is running safely.
Your boiler has detected an internal communication error or a logic failure within the main control system, meaning it cannot verify if it is running safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring Harness
Related codes
14 Your boiler has detected a problem with how it disposes of waste gases, which has caused it to shut down for safety.
Your boiler has detected a problem with how it disposes of waste gases, which has caused it to shut down for safety.
Parts commonly replaced
- Air pressure switch
- Fan assembly
- Venturi tube
- Flue seals
A 01 Your boiler has detected that it has become too hot and has automatically shut itself down to prevent damage.
Your boiler has detected that it has become too hot and has automatically shut itself down to prevent damage.
Parts commonly replaced
- Overheat thermostat
- NTC sensor
- Primary heat exchanger
- Pump
Related codes
A 18 Your boiler is failing to stay lit because the flame keeps going out shortly after it starts.
Your boiler is failing to stay lit because the flame keeps going out shortly after it starts.
Parts commonly replaced
- Flame rectification electrode
- Gas valve
- Ignition lead
Related codes
A 37 Your boiler's main control computer is failing to communicate properly, which has caused the system to shut down for safety.
Your boiler's main control computer is failing to communicate properly, which has caused the system to shut down for safety.
Parts commonly replaced
- Main PCB
- Wiring harness
A 39 Your boiler's main internal computer has detected a critical electronic error that is preventing it from functioning correctly.
Your boiler's main internal computer has detected a critical electronic error that is preventing it from functioning correctly.
Parts commonly replaced
- Main Control Board (PCB)
- Wiring harness
Showing 11–20 of 62
A 40 Your boiler's main computer control panel is experiencing an internal electronic failure, which is preventing the system from operating correctly.
Your boiler's main computer control panel is experiencing an internal electronic failure, which is preventing the system from operating correctly.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
Related codes
A 41 Your boiler has detected an issue with the ventilation system that clears exhaust gases, so it has safely stopped working to prevent any risk.
Your boiler has detected an issue with the ventilation system that clears exhaust gases, so it has safely stopped working to prevent any risk.
Parts commonly replaced
- Fan assembly
- Air pressure switch
- Main circuit board
Related codes
A02 Your boiler has detected a problem with the fan that safely removes exhaust gases, meaning it has shut down as a safety precaution.
Your boiler has detected a problem with the fan that safely removes exhaust gases, meaning it has shut down as a safety precaution.
Parts commonly replaced
- Extraction Fan
- Air Pressure Switch
- Control PCB
Related codes
A03 Your boiler has failed to ignite the flame reliably and has stopped trying for your safety.
Your boiler has failed to ignite the flame reliably and has stopped trying for your safety.
Parts commonly replaced
- Ignition electrode
- Ionisation probe
- Gas valve
- PCB
Related codes
A04 Your boiler is failing to create a spark to ignite the gas, meaning it cannot provide heating or hot water.
Your boiler is failing to create a spark to ignite the gas, meaning it cannot provide heating or hot water.
Parts commonly replaced
- Ignition Electrode
- Ignition Lead
- Printed Circuit Board (PCB)
Related codes
A05 Your boiler is struggling to switch between providing hot water and heating your home due to a jammed internal mechanical part.
Your boiler is struggling to switch between providing hot water and heating your home due to a jammed internal mechanical part.
Parts commonly replaced
- Three-Way Diverter Valve
- Diverter Valve Motor Actuator
Related codes
A06 Your boiler has stopped working because the water is not being pumped around the system properly.
Your boiler has stopped working because the water is not being pumped around the system properly.
Parts commonly replaced
- Circulation pump
- Pump capacitor
- Main PCB
Related codes
A07 Your boiler is failing to detect the flame needed to heat your water, so it has shut down for safety.
Your boiler is failing to detect the flame needed to heat your water, so it has shut down for safety.
Parts commonly replaced
- Flame detection electrode
- Ionisation probe
- Ignition lead
- Printed Circuit Board (PCB)
Related codes
A08 Your boiler has detected an electrical safety issue or a component failure that prevents it from starting up safely.
Your boiler has detected an electrical safety issue or a component failure that prevents it from starting up safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Ignition Electrode
- Wiring Harness
Related codes
A09 Your boiler is struggling to confirm that the burner has lit correctly, causing it to shut down for safety.
Your boiler is struggling to confirm that the burner has lit correctly, causing it to shut down for safety.
Parts commonly replaced
- Ionisation Probe
- Printed Circuit Board (PCB)
- Ignition Electrode
Related codes
Showing 21–30 of 62
A10 Your boiler has failed to detect a flame and has locked out to ensure your safety.
Your boiler has failed to detect a flame and has locked out to ensure your safety.
What to check first
- Check that your gas prepayment meter has credit
- Ensure other gas appliances in your home are working to confirm gas supply
- Press the 'Reset' button on the front of the boiler control panel
Parts commonly replaced
- Ignition Electrode
- Flame Sensing Probe
- Gas Valve
- Printed Circuit Board (PCB)
Related codes
A11 Your boiler's electronic control system has detected an internal electrical failure that prevents it from starting up safely.
Your boiler's electronic control system has detected an internal electrical failure that prevents it from starting up safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Ignition Transformer
Related codes
A12 Your boiler has detected that water is not flowing through the system correctly, likely due to a blockage in the internal filter.
Your boiler has detected that water is not flowing through the system correctly, likely due to a blockage in the internal filter.
Parts commonly replaced
- System Filter
- Central Heating Return Filter
- Circulation Pump
Related codes
B01 Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down before it can be used again.
Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down before it can be used again.
What to check first
- Turn off the boiler and allow it to cool for 20 minutes.
- Ensure all radiator valves are fully open and there is no air trapped in the system.
- Check that the system pressure is between 1.0 and 1.5 bar on the gauge.
- Press the Reset button on the control panel to restart the boiler.
Parts commonly replaced
- Overheat Thermostat
- Circulation Pump
- Main Heat Exchanger
- NTC Temperature Sensor
Related codes
B02 Your boiler is not receiving a signal from your thermostat, which means your heating won't turn on even if you try to increase the temperature.
Your boiler is not receiving a signal from your thermostat, which means your heating won't turn on even if you try to increase the temperature.
What to check first
- Check if your thermostat batteries need replacing.
- Ensure the thermostat is set to 'Heat' and the temperature is set higher than the current room temperature.
- Check that the wireless receiver near the boiler is powered on and has a light showing.
Parts commonly replaced
- Thermostat batteries
- Room thermostat unit
- RF receiver
Related codes
B03 Your boiler's internal mechanism that controls the flame size has failed, meaning the system cannot regulate its heat output properly and has shut down for safety.
Your boiler's internal mechanism that controls the flame size has failed, meaning the system cannot regulate its heat output properly and has shut down for safety.
Parts commonly replaced
- Gas Valve Modulator Coil
- Complete Gas Valve Assembly
- Main Control Board
Related codes
B05 Your boiler has detected a problem with the sensor that monitors the temperature of the water being sent to your radiators, which prevents it from heating your home safely.
Your boiler has detected a problem with the sensor that monitors the temperature of the water being sent to your radiators, which prevents it from heating your home safely.
Parts commonly replaced
- Central Heating (CH) NTC Temperature Sensor
- Sensor Wiring Loom
Related codes
B06 Your boiler has detected that the water pressure inside the system is too low for it to operate safely.
Your boiler has detected that the water pressure inside the system is too low for it to operate safely.
What to check first
- Locate the filling loop (usually a silver braided hose with small valves underneath the boiler).
- Slowly open the valves to allow water into the system while watching the pressure gauge.
- Close the valves firmly once the pressure gauge reaches between 1.0 and 1.5 bar.
Parts commonly replaced
- Low pressure switch
- Filling loop valve
Related codes
B07 Your boiler is having trouble switching between heating your radiators and providing hot water because an internal switch is stuck or failing.
Your boiler is having trouble switching between heating your radiators and providing hot water because an internal switch is stuck or failing.
Parts commonly replaced
- Diverter Valve Microswitch
- Diverter Valve Diaphragm
- Complete Diverter Valve Assembly
Related codes
B08 Your boiler's built-in timer or clock has encountered a communication error, meaning the heating may not turn on at your scheduled times.
Your boiler's built-in timer or clock has encountered a communication error, meaning the heating may not turn on at your scheduled times.
What to check first
- Check the clock settings to ensure they haven't been accidentally cleared
- Rotate the timer pins or digital settings to 'On' to see if the boiler fires
- Perform a simple reset of the boiler using the 'R' or reset button
Parts commonly replaced
- Mechanical Timer Clock
- Digital Programmer
- Control PCB
Related codes
Showing 31–40 of 62
BOILER SHUTDOWN Your boiler has switched itself off completely to prevent damage because a safety sensor has detected a problem with how it is operating.
Your boiler has switched itself off completely to prevent damage because a safety sensor has detected a problem with how it is operating.
What to check first
- Locate the reset button or dial on the front control panel.
- Press or turn the dial to 'Reset' for a few seconds and then release.
- Check if the system pressure gauge is between 1 and 1.5 bar; if low, top up using the filling loop.
Parts commonly replaced
- Overheat Thermostat
- Ignition Electrode
- Printed Circuit Board (PCB)
Related codes
E 05 Your boiler is currently running its built-in frost protection mode to prevent internal parts from freezing, which usually happens during very cold weather.
Your boiler is currently running its built-in frost protection mode to prevent internal parts from freezing, which usually happens during very cold weather.
Related codes
E 06 Your boiler has detected extremely cold conditions and has automatically activated its safety systems to prevent water from freezing inside the pipes.
Your boiler has detected extremely cold conditions and has automatically activated its safety systems to prevent water from freezing inside the pipes.
Parts commonly replaced
- NTC Temperature Sensor
- PCB
Related codes
E 07 Your boiler has detected that hot water isn't moving through your heating pipes properly, so it has shut down to prevent damage.
Your boiler has detected that hot water isn't moving through your heating pipes properly, so it has shut down to prevent damage.
Parts commonly replaced
- Circulation pump
- Flow switch
- Diverter valve
Related codes
E 08 Your boiler has detected that the water level inside the heating system is too low to operate safely.
Your boiler has detected that the water level inside the heating system is too low to operate safely.
What to check first
- Locate the filling loop, which is usually a silver braided hose under the boiler connected to two valves.
- Slowly open the valves to allow mains water into your heating system.
- Watch the pressure gauge on the front of the boiler until it reaches the green zone, typically between 1.0 and 1.5 bar.
- Close both valves tightly and restart the boiler.
Parts commonly replaced
- Filling loop
- Pressure relief valve
- Pressure sensor
Related codes
E 09 Your boiler is currently unable to detect correctly the temperature of your hot water, which means the taps may not heat up as expected.
Your boiler is currently unable to detect correctly the temperature of your hot water, which means the taps may not heat up as expected.
Parts commonly replaced
- Domestic Hot Water (DHW) NTC Thermistor
- Wiring harness
Related codes
E 10 The boiler is unable to read the temperature of your hot water, so it has safely shut down the production of hot water to prevent overheating.
The boiler is unable to read the temperature of your hot water, so it has safely shut down the production of hot water to prevent overheating.
Parts commonly replaced
- DHW NTC sensor
- Wiring harness
Related codes
E 11 Your boiler is failing to detect that water is circulating, which prevents it from safely igniting for your heating or hot water.
Your boiler is failing to detect that water is circulating, which prevents it from safely igniting for your heating or hot water.
Parts commonly replaced
- Flow switch/sensor
- Wiring harness
Related codes
E 12 Your boiler is struggling to detect the flow of water because of a faulty electronic sensor, which will prevent your heating and hot water from working correctly.
Your boiler is struggling to detect the flow of water because of a faulty electronic sensor, which will prevent your heating and hot water from working correctly.
Parts commonly replaced
- DHW Flow Sensor
- Wiring harness
Related codes
E 13 Your boiler has lost the signal from a temperature sensor that monitors the water returning to the system, meaning the unit cannot safely regulate its heat output.
Your boiler has lost the signal from a temperature sensor that monitors the water returning to the system, meaning the unit cannot safely regulate its heat output.
Parts commonly replaced
- Return NTC sensor
- Wiring harness
Related codes
Showing 41–50 of 62
E 14 Your boiler's temperature sensing probe has likely developed a fault, causing the system to misread the water temperature and shut down for safety.
Your boiler's temperature sensing probe has likely developed a fault, causing the system to misread the water temperature and shut down for safety.
Parts commonly replaced
- Return NTC thermistor
- Wiring harness
Related codes
E 15 Your boiler is struggling to read the temperature outside, which is usually due to a loose wire or a damaged sensor cable.
Your boiler is struggling to read the temperature outside, which is usually due to a loose wire or a damaged sensor cable.
Parts commonly replaced
- External temperature sensor
- Wiring loom
Related codes
E 16 Your boiler has lost the signal from the weather sensor installed outside your home, which may cause your heating system to run less efficiently.
Your boiler has lost the signal from the weather sensor installed outside your home, which may cause your heating system to run less efficiently.
Parts commonly replaced
- Outdoor temperature sensor
- Wiring harness
E 18 Your boiler is struggling because the gas flame is jumping away from the burner, which indicates an issue with the air supply or gas pressure balance.
Your boiler is struggling because the gas flame is jumping away from the burner, which indicates an issue with the air supply or gas pressure balance.
Parts commonly replaced
- Gas valve
- Flame sensor
- Air pressure switch
- Flue assembly
Related codes
E 20 Your boiler has detected a flame even though it has commanded the gas supply to shut off, meaning it has safely locked itself to prevent a potential hazard.
Your boiler has detected a flame even though it has commanded the gas supply to shut off, meaning it has safely locked itself to prevent a potential hazard.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Flame rectification electrode
E 29 Your boiler has lost the ability for its internal parts to talk to each other, preventing it from starting up correctly.
Your boiler has lost the ability for its internal parts to talk to each other, preventing it from starting up correctly.
Parts commonly replaced
- Main PCB
- Wiring harness
Related codes
E 30 Your boiler is struggling to send signals between its internal control parts, which has caused it to stop working for your own safety.
Your boiler is struggling to send signals between its internal control parts, which has caused it to stop working for your own safety.
Parts commonly replaced
- Main PCB
- Wiring harness
- Interface cable
Related codes
E 33 Your boiler has stopped because it thinks a safety switch connected to your underfloor heating has been triggered or disconnected.
Your boiler has stopped because it thinks a safety switch connected to your underfloor heating has been triggered or disconnected.
Parts commonly replaced
- Underfloor heating thermostat link
- PCB connection harness
- Safety limit thermostat
E 37 Your boiler's electronic brain is unable to send signals to the system components, causing the boiler to stop working completely.
Your boiler's electronic brain is unable to send signals to the system components, causing the boiler to stop working completely.
Parts commonly replaced
- Main PCB
- Wiring harness
E 38 Your boiler has blocked further attempts to restart itself because the reset button has been pressed too many times in a short window.
Your boiler has blocked further attempts to restart itself because the reset button has been pressed too many times in a short window.
Parts commonly replaced
- PCB
- Control Interface Panel
Related codes
Showing 51–60 of 62
E02 Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
What to check first
- Locate the filling loop, which is usually a metal braided hose underneath the boiler.
- Open the valves on the filling loop to allow cold mains water into the system.
- Watch the pressure gauge on the front of the boiler until it reaches 1.5 bar, then securely close the valves.
Parts commonly replaced
- Pressure relief valve
- Pressure gauge
- Expansion vessel
Related codes
E04 Your boiler is trying to start but the flame is failing to ignite or stay alight, so it has shut down as a safety precaution.
Your boiler is trying to start but the flame is failing to ignite or stay alight, so it has shut down as a safety precaution.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Circuit board (PCB)
- Flame rectification probe
Related codes
Ignition Lockout Your boiler is unable to light the gas flame to provide heating or hot water, and has shut down as a safety precaution.
Your boiler is unable to light the gas flame to provide heating or hot water, and has shut down as a safety precaution.
What to check first
- Check if other gas appliances in your home, like a hob, are working to ensure gas supply.
- Verify that your prepaid gas meter has credit, if applicable.
- Press the Reset button on the control panel to see if the boiler restarts.
Parts commonly replaced
- Ignition Electrode
- Gas Valve
- Printed Circuit Board (PCB)
Related codes
INSUFFICIENT WATER Your boiler has detected that the water pressure is too low to operate safely and has shut down to prevent damage.
Your boiler has detected that the water pressure is too low to operate safely and has shut down to prevent damage.
What to check first
- Locate the filling loop (usually a silver flexible hose) underneath the boiler.
- Slowly open the one or two small taps on the loop until you hear water flowing.
- Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps tightly.
- Turn the selector switch to 'Reset' to clear the fault light.
Parts commonly replaced
- Filling loop valve
- Water pressure switch
- Expansion vessel re-pressurisation
Related codes
L.E.D. B Your boiler is failing to light the gas burner, meaning it cannot provide heating or hot water.
Your boiler is failing to light the gas burner, meaning it cannot provide heating or hot water.
What to check first
- Check if other gas appliances, like a cooker, are working to ensure gas supply is active.
- Check that your prepaid gas meter has enough credit.
- Press the 'Reset' button on the front control panel to attempt a restart.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Spark generator
L.E.D. D Your boiler has detected that water is not moving through the system properly, which is preventing it from heating up safely.
Your boiler has detected that water is not moving through the system properly, which is preventing it from heating up safely.
What to check first
- Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
- If the pressure is below 1 bar, use the filling loop underneath the boiler to top up the water levels.
- Ensure all radiator valves and internal isolation valves are fully open to allow water to flow.
- Reset the boiler once the correct pressure is reached.
Parts commonly replaced
- Circulation Pump
- Primary Pressure Switch
- Automatic Air Vent
L.E.D. G Your boiler has got too hot and has shut itself down as a safety precaution to prevent damage.
Your boiler has got too hot and has shut itself down as a safety precaution to prevent damage.
What to check first
- Wait 30 minutes for the system to cool down completely
- Check that all radiator valves are fully open to allow water flow
- Turn the selector switch to the 'Reset' position and then back to 'On'
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Main Heat Exchanger
Limescale Build-up Your boiler is limiting its temperature to prevent damage because it has detected a buildup of limescale in the system.
Your boiler is limiting its temperature to prevent damage because it has detected a buildup of limescale in the system.
Parts commonly replaced
- Secondary Plate Heat Exchanger
- DHW Temperature Sensor (NTC)
PUMP SAFETY DEVICE ACTIVATED Your boiler has detected that water is not circulating correctly, which has triggered a safety shutdown to prevent the unit from overheating.
Your boiler has detected that water is not circulating correctly, which has triggered a safety shutdown to prevent the unit from overheating.
What to check first
- Check that your system pressure is between 1 and 1.5 bar on the pressure gauge.
- Ensure all radiator valves are fully open to allow water flow.
- Try resetting the boiler to see if the fault was a temporary air lock.
Parts commonly replaced
- Circulation Pump
- Differential Pressure Switch
- Printed Circuit Board (PCB)
Related codes
Red L.E.D. B Your boiler has failed to ignite and has locked itself out for safety reasons, meaning you will not have any heating or hot water until it is reset.
Your boiler has failed to ignite and has locked itself out for safety reasons, meaning you will not have any heating or hot water until it is reset.
What to check first
- Locate the reset button 'A' on the control panel.
- Press and release the reset button to see if the boiler restarts.
- Check if your gas supply is active by testing other gas appliances like a hob.
Parts commonly replaced
- Ignition Electrode
- Gas Valve
- Printed Circuit Board (PCB)
Showing 61–62 of 62
Red L.E.D. G Your boiler has switched itself off because it has become too hot to operate safely.
Your boiler has switched itself off because it has become too hot to operate safely.
What to check first
- Check that all radiator valves are fully open to allow water to circulate
- Inspect the system pressure gauge and top up to 1.5 bar if it is low
- Press the Reset button once the boiler has had 15 minutes to cool down
- Ensure that the condensate pipe is not frozen if it is winter
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Main Heat Exchanger
Safety Shut-off Your boiler has failed its internal safety check and has shut itself down to prevent a fault from becoming more serious.
Your boiler has failed its internal safety check and has shut itself down to prevent a fault from becoming more serious.
What to check first
- Locate the Reset button on the control panel
- Press and hold the Reset button for five seconds
- Wait for the boiler to attempt to restart; if it fails again, do not continue to reset
Parts commonly replaced
- Printed Circuit Board (PCB)
- Ignition Electrode
- Gas Valve