Ariston Alteas One Fault codes & diagnostics

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

Combi Natural GasLPG 24 kW 2017-present

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Severity at a glance

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42 High 12 Medium 3 Low
Just want the most common Ariston Alteas One faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 57 documented codes

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1p1

Your boiler has detected that water is not circulating properly, which is causing it to stop to prevent overheating.

High DIY-safe £180-350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the gauge.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Bleed your radiators to remove any trapped air that might be blocking water flow.
  4. Reset the boiler using the 'Reset' button on the front panel.

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (de-scaling)
  • Flow/Return thermistors

Related codes

Full explanation for 1p1
1p2

Your boiler is not circulating water correctly, meaning it is sensing that the temperature is rising too quickly and has stopped to prevent overheating.

High DIY-safe £120-350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the display.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Bleed your radiators to remove any trapped air that might be blocking water flow.

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (flushing/cleaning)
  • Flow/Return thermistors

Related codes

Full explanation for 1p2
1p3

Your boiler is struggling to circulate water properly, which is causing it to overheat and shut down temporarily for safety.

Medium DIY-safe £100-£350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the display.
  2. Ensure all radiator valves are fully open to allow water to flow.
  3. Gently bleed your radiators to remove any trapped air pockets.

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (de-scaling)
  • Flow/Return thermistors

Related codes

Full explanation for 1p3
1p4

Your boiler is struggling to circulate water effectively, which is causing it to shut down to prevent overheating.

High DIY-safe £120-£350

What to check first

  1. Check if your radiator valves are fully open
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar
  3. Try resetting the boiler using the 'Reset' button

Parts commonly replaced

  • Main Heat Exchanger (Cleaning/Descaling)
  • Circulation Pump
  • Flow/Return Thermistors

Related codes

Full explanation for 1p4
3P9

Your boiler has detected that it is time for a scheduled routine maintenance service to ensure it continues running safely and efficiently.

Low Engineer only £80-£120

Parts commonly replaced

  • None (Maintenance procedure)
  • Seals or gaskets if required during service
Full explanation for 3P9
5P1

Your boiler is struggling to light properly after several attempts, usually due to an unreliable gas supply or a slightly dirty component.

High Engineer only £100-250

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve

Related codes

Full explanation for 5P1
5P2

Your boiler is struggling to light its flame properly, which means it will stop working to keep you safe.

High Engineer only £120-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Detection electrode

Related codes

Full explanation for 5P2
5P3

Your boiler has lost its flame suddenly during operation, causing it to stop Working as a safety precaution.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation probe
  • Spark electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for 5P3
101

Your boiler has stopped working because it has detected an overheating issue within the main heat exchanger.

High DIY-safe £120-350

What to check first

  1. Turn the boiler off and allow it to cool down for 20 minutes.
  2. Ensure all radiator valves are fully open and there are no obstructions to water flow.
  3. Press the 'Reset' button on the front control panel to restart the system.

Parts commonly replaced

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

Related codes

Full explanation for 101
102

Your boiler has lost its connection to the internet or smart control system, meaning you can't control it via the app, although the heating may still work manually.

Low DIY-safe £0-60

What to check first

  1. Check that your home Wi-Fi router is turned on and working.
  2. Try restarting your Wi-Fi router and wait five minutes.
  3. Reset the boiler's connectivity settings via the display menu.

Parts commonly replaced

  • Wi-Fi Gateway module
  • External antenna

Related codes

Full explanation for 102
Showing 11–20 of 57
103

Your boiler is likely having trouble circulating water properly, which is causing it to overheat and shut down for safety.

High DIY-safe £150-350

What to check first

  1. Check that your system pressure is between 1 and 1.5 bar on the display.
  2. Ensure all radiator valves are fully open to allow water to flow.
  3. Attempt to reset the boiler once pressure and valves are checked.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Cleaning)
  • Flow/Return Temperature Sensors

Related codes

Full explanation for 103
104

Your boiler is struggling to circulate water properly, which is preventing it from heating up safely.

High DIY-safe £100-350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the display.
  2. If the pressure is low, use the filling loop to top it up.
  3. Ensure all radiator valves and isolation valves under the boiler are fully open.
  4. Reset the boiler after checking these steps.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Cleaning)
  • Pump Lead

Related codes

Full explanation for 104
105

Your boiler has detected that water is not circulating properly, causing it to overheat and shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the gauge.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Try bleeding your radiators to remove any trapped air pockets.
  4. Restart the boiler using the reset button.

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger
  • Temperature sensors (NTC thermistors)

Related codes

Full explanation for 105
106

Your boiler has detected that there is not enough water pressure or circulation to function properly and has shut down for safety.

High DIY-safe £60-120

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. If the pressure is too low, use the built-in filling loop (often blue levers underneath) to top up the water level.
  3. Ensure all radiator valves are fully open and restart the boiler using the reset button.

Parts commonly replaced

  • External filling loop
  • Pressure sensor
  • Circulation pump

Related codes

Full explanation for 106
107

Your boiler has detected that water is not circulating properly through the system, often caused by trapped air or a blockage.

High DIY-safe £100-£350

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 is between 1 and 1.5 bar

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Pump Cable Harness

Related codes

Full explanation for 107
108

Your boiler has detected that the water pressure is too low, which prevents it from operating safely to provide heating or hot water.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually blue levers or a pull-down tap) underneath the boiler.
  2. Slowly open the valves until you hear water entering the system and watch the pressure gauge.
  3. Close both valves tightly once the pressure reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 108
109

Your boiler has detected that the water is circulating poorly or there is trapped air, causing it to shut down to prevent overheating.

High DIY-safe £120-£350

What to check first

  1. Check that the boiler pressure is between 1 and 1.5 bar on the gauge.
  2. Ensure all radiator valves are fully open.
  3. Bleed your radiators to remove any trapped air from the system.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Cleaning)
  • Automatic Air Vent

Related codes

Full explanation for 109
110

Your boiler has detected that it is getting too hot, so it has shut down to prevent any damage to the internal components.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1 and 1.5 bar on the gauge
  3. Try resetting the boiler using the 'Reset' button on the front panel

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger

Related codes

Full explanation for 110
112

Your boiler is having trouble moving water through the system properly, which has stopped it from heating up safely.

High DIY-safe £120-350

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the display
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Gently bleed your radiators to remove trapped air
  4. Reset the boiler using the 'Reset' button on the touch screen

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (cleaning or replacement)
  • Return Filter

Related codes

Full explanation for 112
114

Your boiler has detected a problem with its external temperature sensor, which helps it understand how hard it needs to work based on the weather outside.

Low Engineer only £90-160

Parts commonly replaced

  • External temperature sensor
  • Wiring harness

Related codes

Full explanation for 114
Showing 21–30 of 57
116

Your boiler has detected that the floor heating thermostat has tripped to prevent overheating in that specific circuit.

Medium Engineer only £90-180

Parts commonly replaced

  • Overheat thermostat
  • External zone valve
  • Wiring loom

Related codes

Full explanation for 116
118

Your boiler has detected that the water pressure is too high, often caused by the filling loop being left open or a fault in the expansion system.

High DIY-safe £80-220

What to check first

  1. Check that the filling loop valves are tightly closed
  2. Bleed water from a radiator using a bleed key to reduce the system pressure
  3. Monitor the pressure gauge to ensure it returns to between 1 and 1.5 bar
  4. Reset the boiler once the pressure is stabilised

Parts commonly replaced

  • Pressure Relief Valve (PRV)
  • Expansion Vessel
  • Filling Loop Tap

Related codes

Full explanation for 118
202

Your boiler is having trouble communicating with the digital display or control panel, preventing it from functioning correctly.

High Engineer only £120-£350

Parts commonly replaced

  • Main PCB
  • Display Interface Board
  • Wiring harness

Related codes

Full explanation for 202
204

Your boiler has lost its connection to the system's display screen or control board, meaning it cannot receive or process instructions properly.

High Engineer only £150-450

Parts commonly replaced

  • Main PCB
  • LCD Display Board
  • Wiring Harness

Related codes

Full explanation for 204
205

Your boiler has lost the wireless or wired communication with its external temperature sensor, meaning it doesn't know how hard it needs to work to heat your home.

Medium DIY-safe £90-180

What to check first

  1. Check if your outdoor sensor has any visible damage or loose wires.
  2. If the sensor is wireless, replace the batteries in the external unit.
  3. Reset the boiler by pressing the 'Reset' button on the front panel.

Parts commonly replaced

  • External Temperature Sensor
  • Sensor Wiring
  • PCB (in rare cases)

Related codes

Full explanation for 205
207

Your boiler has lost communication with its smart controls or sensors, meaning it cannot receive the correct instructions to heat your home.

High DIY-safe £100-250

What to check first

  1. Turn the boiler power off and back on at the fused spur switch to reset the internal electronics
  2. Check that your external thermostat or smart Hub is powered and connected to your Wi-Fi
  3. Press the 'Reset' button on the boiler front panel

Parts commonly replaced

  • Main PCB
  • Communication Gateway
  • Wiring Harness

Related codes

Full explanation for 207
208

Your boiler is unable to provide heating or hot water because it has detected that the solar collector sensor has a short circuit or is disconnected.

High Engineer only £90-180

Parts commonly replaced

  • Solar temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for 208
301

Your boiler's main control board has detected a communication error or internal software fault and requires a reset or professional inspection.

High DIY-safe £180-450

What to check first

  1. Locate the Reset button on the front control panel.
  2. Press and hold the Reset button for 5 seconds.
  3. Wait for the boiler to complete its restart sequence.

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display Interface Unit

Related codes

Full explanation for 301
302

Your boiler has lost its connection between the main control board and the display panel, meaning they can no longer talk to each other.

High Engineer only £120-350

Parts commonly replaced

  • Display PCB
  • Main Circuit Board
  • Wiring Harness

Related codes

Full explanation for 302
303

Your boiler's main control board has detected an internal electronic error and has shut down as a safety precaution.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 303
Showing 31–40 of 57
304

Your boiler has attempted to restart itself too many times in a short period and has temporarily locked you out for safety.

Medium DIY-safe £0-120

What to check first

  1. Locate the Reset button on the front control panel.
  2. Press and hold the Reset button for 5 seconds.
  3. Wait for the boiler to complete its restart sequence.
  4. If the code persists, check if other gas appliances are working.

Parts commonly replaced

  • No parts usually required
  • Spark Electrode
  • Ignition Lead

Related codes

Full explanation for 304
305

Your boiler's main control board has encountered an internal electronic error and needs to be reset.

High DIY-safe £250-450

What to check first

  1. Locate the Reset button on the front control panel.
  2. Press and hold the Reset button for five seconds.
  3. Wait for the boiler to complete its restart sequence.

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 305
306

Your boiler's main control board has detected an internal electronic error and has shut down as a safety precaution.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 306
307

Your boiler’s main control board has encountered an internal software or data error and cannot communicate correctly.

High DIY-safe £250-450

What to check first

  1. Locate the power switch or fused spur for the boiler
  2. Turn the power off, wait for 60 seconds, and turn it back on
  3. Press the Reset button on the boiler front panel once the display restarts

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • EEPROM chip

Related codes

Full explanation for 307
407

Your boiler has lost its connection to the room thermostat, meaning it cannot receive the signal to turn your heating on or off.

High DIY-safe £0-120

What to check first

  1. Check the batteries in your room thermostat and replace them if they are low.
  2. Ensure the thermostat is within range of the boiler and has not been moved behind a metal object.
  3. Try resetting the boiler by pressing the 'Reset' button on the front panel.

Parts commonly replaced

  • Thermostat batteries
  • RF Receiver
  • Room Thermostat unit
Full explanation for 407
411

Your boiler has lost communication with the main thermostat or temperature sensor in your primary living area, meaning it doesn't know when to turn the heating on or off.

Medium DIY-safe £90-180

What to check first

  1. Check if your room thermostat or sensor has run out of batteries and replace them if necessary.
  2. Ensure the thermostat is within range of the boiler and has not been moved behind a large metal object or thick wall.
  3. Try restarting the boiler using the Reset button to refresh the sensor connection.

Parts commonly replaced

  • Room thermostat batteries
  • Wall-mounted room sensor
  • RF Receiver

Related codes

Full explanation for 411
412

Your boiler has lost communication with the temperature sensor controlling your second heating zone, meaning it can no longer regulate the heat for those specific rooms.

Medium Engineer only £90-180

Parts commonly replaced

  • Room thermostat
  • Zone 2 temperature sensor
  • Connection wiring

Related codes

Full explanation for 412
414

Your boiler has lost communication with the temperature sensor that controls the heating for the third zone in your home.

Medium Engineer only £90-180

Parts commonly replaced

  • Zone 3 Room Sensor
  • Wiring Loom
  • Zone Control Modulating Board

Related codes

Full explanation for 414
501

Your boiler has failed to light the flame, which means you will not have any heating or hot water until the issue is resolved.

High DIY-safe £90-250

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching the property.
  2. Inspect the white plastic condensate pipe outside; if it is frozen, gently thaw it with warm water.
  3. Press the 'Reset' button on the front panel to attempt to restart the ignition sequence.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB

Related codes

Full explanation for 501
502

Your boiler has detected a flame when there shouldn't be one, which is causing the system to lock out for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 502
Showing 41–50 of 57
504

Your boiler has detected that the flame has gone out several times unexpectedly, which has caused it to stop working for safety.

High DIY-safe £90-280

What to check first

  1. Press the Reset button on the front control panel
  2. Check that your gas pre-payment meter (if you have one) has credit
  3. Ensure other gas appliances in your home, such as a hob, are still working correctly

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve

Related codes

Full explanation for 504
604

Your boiler's fan is running too slowly, which prevents the system from safely starting up to provide heating and hot water.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 604
610

Your boiler's control system has detected an internal electronic error, often caused by a communication failure between the sensors and the main circuit board.

High Engineer only £180-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness
  • NTC Sensor

Related codes

Full explanation for 610
612

Your boiler's fan is not spinning at the correct speed, which prevents the unit from starting up safely for heating or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Main PCB
  • Wiring harness

Related codes

Full explanation for 612
701

Your boiler has detected a fault with the heating zone 1 flow temperature sensor, which means it cannot accurately monitor the water temperature leaving the boiler.

Medium Engineer only £90-160

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for 701
702

Your boiler has detected a communication error between its internal control boards or with an external sensing component, causing it to stop working.

High Engineer only £160-320

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display PCB
  • Wiring Loom

Related codes

Full explanation for 702
703

Your boiler has detected a communication problem between its main control board and the display panel, meaning the internal components cannot talk to each other properly.

High Engineer only £120-£350

Parts commonly replaced

  • Display PCB
  • Main Control PCB
  • Wiring Loom

Related codes

Full explanation for 703
704

Your boiler has detected an internal communication error between its main control boards, meaning it can no longer send or receive instructions correctly.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Display Interface PCB
  • Wiring Harness

Related codes

Full explanation for 704
705

Your boiler is having trouble communicating with the internal electronic controls, meaning it cannot process instructions to heat your home.

High Engineer only £180-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Display Interface PCB
  • Wiring Loom

Related codes

Full explanation for 705
706

Your boiler has stopped working because its internal computer is struggling to communicate with the main control board.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Ribbon Cable

Related codes

Full explanation for 706
Showing 51–57 of 57
707

Your boiler has detected an internal communication failure between the electronic control boards, meaning the main system cannot talk to its secondary controls.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Display Interface PCB
  • Communication Wiring Loom

Related codes

Full explanation for 707
711

Your boiler has lost track of the temperature of the water coming back from your radiators, which may stop your heating from working efficiently or starting up at all.

High Engineer only £90-160

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Wiring harness connecting the sensor

Related codes

Full explanation for 711
712

Your boiler is struggling to monitor the temperature of the water returning from the second heating zone, which may prevent some of your radiators from warming up correctly.

Medium Engineer only £110-190

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Wiring harness / Connector

Related codes

Full explanation for 712
713

Your boiler has lost the ability to monitor the temperature of water returning from your third heating zone, which may prevent that specific area from heating up correctly.

Medium Engineer only £120-£200

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for 713
722

Your boiler has detected that the secondary heating circuit is getting too hot, likely due to a circulation or sensor issue.

Medium DIY-safe £120-280

What to check first

  1. Check that all radiator valves in the secondary zone (e.g. upstairs or underfloor heating) are fully open.
  2. Ensure there is no trapped air in the system by bleeding the radiators.
  3. Restart the boiler to see if the fault clears.

Parts commonly replaced

  • Zone 2 NTC temperature sensor
  • Zone pump
  • Three-way valve

Related codes

Full explanation for 722
723

Your boiler has detected that the third heating zone is getting too hot, likely due to a circulation problem or a faulty sensor in that specific area of your home.

Medium DIY-safe £120-250

What to check first

  1. Check that all radiator valves in Zone 3 are open and not turned off.
  2. Ensure there are no obstructions around any localized zone pumps or valves.
  3. Try resetting the boiler to see if the error was a temporary sensor glitch.

Parts commonly replaced

  • Zone NTC sensor
  • Zone 3 circulating pump
  • Motorised zone valve

Related codes

Full explanation for 723
750

Your boiler has disabled all heating areas, meaning your radiators will not warm up until the control system is reset or communicating correctly.

High DIY-safe £100-280

What to check first

  1. Locate the 'Reset' button on the front touch display
  2. Press and hold Reset for 3-5 seconds
  3. Wait for the boiler to complete its reboot cycle to see if the central heating resumes

Parts commonly replaced

  • Main PCB
  • Zone Management Kit
  • External Controller/Thermostat

Related codes

Full explanation for 750