Ariston E-Combi One 24 Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2019-present

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Severity at a glance

Each cell = one fault code. Hover to identify.
31 High 12 Medium 3 Low
Just want the most common Ariston E-Combi One 24 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 46 documented codes

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1 01

Your boiler has become too hot and has shut itself down as a safety precaution to prevent internal damage.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure your system pressure is between 1 and 1.5 bar on the pressure gauge.
  3. Press the Reset button on the front control panel and wait for the boiler to restart.

Parts commonly replaced

  • Central heating pump
  • Overheat thermostat
  • Main heat exchanger (flushing)

Related codes

Full explanation for 1 01
1 03

Your boiler is struggling to move water around the system properly, causing it to shut down to prevent overheating.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves (TRVs) are turned to the highest setting
  2. Ensure your boiler pressure is between 1 and 1.5 bar on the gauge
  3. Try bleeding your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger
  • Central heating filter

Related codes

Full explanation for 1 03
1 04

Your boiler is struggling to move water through the system efficiently, which usually means the water pressure is too low or something is blocking the flow.

High DIY-safe £80-250

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 pressure is low, use the filling loop underneath the boiler to top it up.
  3. Ensure all radiator valves are fully open and bleed any radiators that have trapped air.

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger (flushing/cleaning)
  • Water pressure sensor

Related codes

Full explanation for 1 04
1 05

Your boiler has stopped working because water is not moving through the system quickly enough to prevent it from getting too hot.

High DIY-safe £150-350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure your boiler pressure is between 1 and 1.5 bar
  3. Gently bleed your radiators to remove trapped air

Parts commonly replaced

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

Related codes

Full explanation for 1 05
1 06

Your boiler is struggling to move water through the system, which is causing it to shut down to prevent overheating.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar
  3. Gently bleed your radiators to remove any trapped air

Parts commonly replaced

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

Related codes

Full explanation for 1 06
1 07

Your boiler is struggling to move hot water around the system, often caused by trapped air or low pressure preventing it from flowing correctly.

High DIY-safe £80-250

What to check first

  1. Check the pressure gauge and top up to 1.5 bar if it is low
  2. Bleed all radiators to remove any trapped air pockets
  3. Ensure all radiator valves and the boiler isolation valves are fully open

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Pump Auto Air Vent

Related codes

Full explanation for 1 07
1 08

Your boiler has lost water pressure and needs to be topped up to work properly again.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually blue levers) underneath the boiler.
  2. Slowly open both levers until you hear water flowing into the system.
  3. Watch the pressure gauge and close the levers firmly when it reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 1 08
1 09

Your boiler has too much water inside its system, causing it to shut down to prevent damage from high pressure.

High DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are fully closed and not letting in water
  2. Bleed water from a radiator using a bleed key to reduce the system pressure
  3. Monitor the pressure gauge until it returns to between 1 and 1.5 bar
  4. Restart the boiler once the pressure is within the normal operating range

Parts commonly replaced

  • Filling loop valve
  • Pressure relief valve (PRV)
  • Expansion vessel

Related codes

Full explanation for 1 09
1 10

Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely control your heating.

High Engineer only £90-160

Parts commonly replaced

  • C.H. Flow NTC Temperature Probe
  • Wiring Harness Connection

Related codes

Full explanation for 1 10
1 12

Your boiler has detected a fault with the sensor that monitors the temperature of the water returning from your radiators, meaning it cannot operate safely.

High Engineer only £100-£180

Parts commonly replaced

  • Central Heating Return NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for 1 12
Showing 11–20 of 46
1 14

Your boiler has lost connection with the sensor that measures the temperature outside, which helps it run more efficiently.

Low Engineer only £80-160

Parts commonly replaced

  • External weather compensation sensor
  • Sensor wiring

Related codes

Full explanation for 1 14
1 16

Your boiler has detected that a safety device designed to prevent your underfloor heating from overheating has been triggered and cut the connection.

High Engineer only £90-180

Parts commonly replaced

  • Floor thermostat sensor
  • Overheat safety stat
  • Wiring harness

Related codes

Full explanation for 1 16
1 18

Your boiler has detected a fault with the sensor that monitors the temperature of the water being sent to your radiators, causing the system to stop working for safety.

High Engineer only £120-190

Parts commonly replaced

  • NTC Temperature Probe
  • Flow Thermistor
  • Wiring Harness

Related codes

Full explanation for 1 18
1 P1

Your boiler is struggling to move water through the system efficiently, which is stopping it from heating up correctly.

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. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Try bleeding your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Cleaning/Powerflush)
  • Water Pressure Sensor

Related codes

Full explanation for 1 P1
1 P2

Your boiler is struggling to move water through the system properly, which is causing it to stop running 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 display
  2. Ensure all radiator valves are fully open to allow water to flow
  3. Check for any visible leaks around the pipework or radiators

Parts commonly replaced

  • Main Circulation Pump
  • Central Heating Filter
  • Primary Heat Exchanger (if blocked)

Related codes

Full explanation for 1 P2
1 P3

Your boiler is struggling to move water through the system properly, which is preventing it from heating up correctly.

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 are fully open
  3. Bleed your radiators to remove any trapped air

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger (de-scaling)
  • Central heating filter

Related codes

Full explanation for 1 P3
1 P4

Your boiler is struggling to push water through the system, which is causing it to stop running to prevent overheating.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Bleed your radiators to remove any trapped air
  4. Reset the boiler using the 'R' button

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Cleaning)
  • Central Heating Filter

Related codes

Full explanation for 1 P4
2 05

Your boiler is having trouble measuring the temperature of the water coming from your solar thermal system or incoming supply, which can affect how your hot water is heated.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) Inlet NTC Sensor
  • Sensor Wiring Harness
Full explanation for 2 05
3 01

Your boiler's internal computer memory has encountered a software error, meaning the control board cannot process settings correctly.

High Engineer only £220-400

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display PCB

Related codes

Full explanation for 3 01
3 02

Your boiler's internal computer system has lost communication with the display screen, meaning the components cannot talk to each other to start the heating process.

High DIY-safe £120-350

What to check first

  1. Press the Reset button on the front panel and wait for the boiler to reboot
  2. Switch off the electrical power supply to the boiler at the fused spur for 30 seconds, then switch it back on

Parts commonly replaced

  • Display PCB unit
  • Main Control PCB
  • Wiring loom connection

Related codes

Full explanation for 3 02
Showing 21–30 of 46
3 03

Your boiler’s main internal control board has developed a technical fault, preventing the system from starting up or operating safely.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 3 03
3 04

Your boiler has been manually reset more than five times in fifteen minutes and has temporarily locked itself for safety.

Medium DIY-safe £0-120

What to check first

  1. Turn off the power supply to the boiler at the fused spur switch.
  2. Wait for at least 15 minutes without touching any buttons to allow the internal timer to reset.
  3. Turn the power back on and see if the boiler resumes normal operation.

Parts commonly replaced

  • No parts usually required
  • Printed Circuit Board (PCB) if the error persists

Related codes

Full explanation for 3 04
3 05

Your boiler's main control board has encountered an internal electronic failure and can no longer manage the system's functions.

High Engineer only £280-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 3 05
3 06

Your boiler's electronic control centre has developed a technical fault and cannot communicate with the rest of the system.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 3 06
3 07

Your boiler's internal computer has developed a fault and can no longer communicate with the rest of the system.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 3 07
3 P9

Your boiler is simply reminding you that its annual service is due soon to ensure it continues running safely and efficiently.

Low Engineer only £80-120

Parts commonly replaced

  • None (Standard Service)
  • Burner Gasket (often replaced during service)
Full explanation for 3 P9
4 11

Your boiler has lost communication with the main thermostat or room sensor, meaning it doesn't know when to turn the heating on or off.

Medium DIY-safe £0-120

What to check first

  1. Check if your wireless thermostat 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 metal object.
  3. Try resetting the boiler by pressing the 'Reset' button on the front panel.

Parts commonly replaced

  • Thermostat batteries
  • Room thermostat / RF Receiver
  • Sensor wiring

Related codes

Full explanation for 4 11
4 12

Your boiler has lost communication with the temperature sensor that controls your second heating zone, meaning it can't tell how warm that part of your home is.

Medium Engineer only £90-180

Parts commonly replaced

  • Zone 2 Room Sensor
  • Wiring Loom
  • Zone Control PCB

Related codes

Full explanation for 4 12
4 13

Your boiler has lost communication with the temperature sensor responsible for controlling the heating in your third heating zone.

Medium Engineer only £100-£190

Parts commonly replaced

  • Room thermostat
  • External sensor wiring
  • Zone interface PCB

Related codes

Full explanation for 4 13
5 01

Your boiler is failing to light the gas even though it is trying to start up.

High DIY-safe £120-350

What to check first

  1. Check if your gas supply is turned on at the meter
  2. Check if other gas appliances in your home are working
  3. Press the Reset button once to see if the boiler restarts

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • Condensate Trap

Related codes

Full explanation for 5 01
Showing 31–40 of 46
5 02

Your boiler thinks a flame is present even though no gas should be flowing, which is a safety precaution that stops it from starting up.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation probe
  • Gas valve
  • Main PCB

Related codes

Full explanation for 5 02
5 04

Your boiler is struggling to keep the flame lit because it is drifting away from the burner, causing the system to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation probe
  • Gas valve
  • Burner gasket

Related codes

Full explanation for 5 04
5 P1

Your boiler tried to start up but couldn't create a flame on its first attempt, meaning you likely have no heating or hot water right now.

High DIY-safe £100-280

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a prepaid gas meter, ensure you have sufficient credit
  3. Press the Reset button on the control panel to allow the boiler to try again

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve

Related codes

Full explanation for 5 P1
5 P2

Your boiler has failed to light after two attempts, which means it will not provide heating or hot water until the issue is resolved.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home, like a gas hob, are working correctly to ensure gas supply.
  2. Inspect the outdoor condensate pipe to see if it is frozen or blocked.
  3. Press the Reset button on the front control panel to allow the boiler to try lighting again.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Generator

Related codes

Full explanation for 5 P2
5 P3

Your boiler is struggling to keep a steady flame alight, causing it to stop running for safety reasons.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for 5 P3
6 10

Your boiler has shut down because the internal water temperature has become too hot, likely due to a blockage or a pump failure.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are open to allow water to circulate.
  2. Ensure the system pressure is between 1 and 1.5 bar on the gauge.
  3. Restart the boiler using the Reset button.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Overheat Thermostat

Related codes

Full explanation for 6 10
6 12

Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.

High Engineer only £180-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Venturi tube

Related codes

Full explanation for 6 12
7 01

Your boiler has detected a fault with a temperature sensor in your main heating circuit, which may prevent your radiators from warming up correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 7 01
7 02

Your boiler has detected a fault with a temperature sensor responsible for controlling one of your heating zones, which may cause that specific area of your home to stop heating correctly.

Medium Engineer only £100-£180

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 7 02
7 03

Your boiler has detected a fault with a temperature sensor in the third heating zone, meaning it can no longer accurately measure or control the heat for that specific area.

Medium Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness
  • Zone expansion PCB

Related codes

Full explanation for 7 03
Showing 41–46 of 46
7 11

Your boiler has detected a faulty temperature sensor on the return pipe of your primary heating circuit, which may prevent the system from knowing how hot the water is as it returns to the boiler.

Medium Engineer only £90-160

Parts commonly replaced

  • Zone 1 Return NTC Sensor
  • Wiring Harness

Related codes

Full explanation for 7 11
7 12

Your boiler has detected a faulty sensor responsible for monitoring the temperature of the water returning from your secondary heating zone, which may prevent that specific area from heating correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • NTC Return Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 7 12
7 13

Your boiler has detected a technical fault with a temperature sensor in part of your heating system, though your primary heating and hot water may still function.

Low Engineer only £90-160

Parts commonly replaced

  • Zone return NTC sensor
  • Sensor wiring harness

Related codes

Full explanation for 7 13
7 22

Your home's secondary heating area has become too hot, causing the boiler to shut down that specific part of the system for safety.

Medium DIY-safe £100-250

What to check first

  1. Check that all radiator valves in Zone 2 are fully open and not turned to zero.
  2. Ensure there are no obstructions around the vents or localized heaters in that zone.
  3. Try resetting the boiler via the 'Reset' button on the front panel.

Parts commonly replaced

  • Zone valve
  • Secondary heating zone sensor (NTC)
  • External pump

Related codes

Full explanation for 7 22
7 23

Your boiler has detected that the water in the third heating area of your home is getting too hot and has shut down to protect itself.

Medium DIY-safe £120-280

What to check first

  1. Check that all radiator valves in Zone 3 are fully open
  2. Ensure the heating zone valves are not stuck in the closed position
  3. Check if the pump for that specific zone is running

Parts commonly replaced

  • Zone Valve
  • External Circulating Pump
  • Overheat Thermostat

Related codes

Full explanation for 7 23
7 50

Your boiler has disabled your heating system across all zones because it cannot detect a valid control signal or has experienced a communication failure between the thermostats and the main unit.

High DIY-safe £0-120

What to check first

  1. Check that your room thermostats or smart heating controls have working batteries.
  2. Ensure your internet router is on if you use Ariston Net or smart controls.
  3. Turn the boiler off and on again at the fused spur switch to reset the communication bus.
  4. Verify that the heating schedule on your app or programmer is not accidentally set to 'Off'.

Parts commonly replaced

  • Thermostat batteries
  • RF Receiver
  • Bus interface module

Related codes

Full explanation for 7 50