Ariston Clas ONE R Fault codes & diagnostics

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

Regular Natural Gas 2020-present
GC Number 41-116-52
Download the Ariston Clas ONE R manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 9 High 4 Medium
Just want the most common Ariston Clas ONE R faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 14 documented codes

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1P4

Your boiler has detected that water is not flowing around your heating system as efficiently as it should be.

High DIY-safe £100-250

What to check first

  1. Check your central heating pressure gauge; if it is below 1 bar, top it up using the filling loop
  2. Ensure all radiator valves are fully open to allow water to circulate freely
  3. Restart the boiler to reset the system after adjusting pressure or valves

Parts commonly replaced

  • Circulation pump
  • Flow sensor
  • Heating system filter

Related codes

Full explanation for 1P4
3 05

Your boiler's computer is experiencing an internal communication error and has safely shut itself down to prevent further issues.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB

Related codes

Full explanation for 3 05
3 06

Your boiler's internal computer is experiencing a communication error and cannot operate safely, meaning your heating and hot water will be unavailable.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

Full explanation for 3 06
7 11

Your boiler is struggling to accurately measure the temperature of the water returning from your heating system, which is preventing it from heating your home correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for 7 11
7 12

Your boiler is having trouble reading the water temperature for your secondary heating circuit, which may prevent that specific zone from heating up properly.

Medium Engineer only £120-200

Parts commonly replaced

  • NTC return sensor
  • Wiring harness

Related codes

Full explanation for 7 12
7 13

Your boiler is having trouble communicating with the temperature sensor for one of your heating zones, which may stop that specific area from heating correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • NTC return sensor
  • Wiring harness

Related codes

Full explanation for 7 13
7 23

Your boiler has detected that the water temperature in one of your heating zones is higher than the system is designed to handle, so it has stopped that zone to prevent damage.

Medium Engineer only £120-250

Parts commonly replaced

  • NTC temperature sensor
  • Zone valve
  • Main PCB

Related codes

Full explanation for 7 23
106

Your boiler has stopped working because the water returning from your radiators is significantly hotter than the water leaving the boiler, suggesting the water isn't flowing correctly.

High DIY-safe £120-350

What to check first

  1. Ensure all radiator valves (TRVs) are turned to the highest setting
  2. Check that at least one radiator or bypass valve is fully open
  3. Bleed all radiators to remove trapped air locks

Parts commonly replaced

  • Circulation Pump
  • Return Temperature Sensor (NTC)
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for 106
108

Your boiler has lost water pressure and has shut down to prevent damage, meaning it simply needs to be refilled to the correct level.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually blue handles or a small plastic key) underneath the boiler.
  2. Slowly open the valves until you hear water entering the system.
  3. Watch the pressure gauge and close the valves tightly once it reaches 1.5 bar.
  4. The error code should clear automatically; if not, press the 'Reset' button.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Auto air vent

Related codes

Full explanation for 108
109

Your boiler has too much water pressure inside the system, causing it to shut down for safety.

Emergency DIY-safe £80-200

What to check first

  1. Check that the filling loop valves under the boiler are tightly closed.
  2. Bleed water from a radiator using a bleed key until the pressure gauge on the boiler falls back between 1 and 1.5 bar.
  3. Restart the boiler once the pressure is stabilised.

Parts commonly replaced

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

Related codes

Full explanation for 109
116

Your boiler has detected that the safety sensor for an underfloor heating circuit has tripped to prevent the floor from overheating.

High Engineer only £90-180

Parts commonly replaced

  • Floor thermostat
  • Overheat limit thermostat
  • Wiring harness

Related codes

Full explanation for 116
118

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

High Engineer only £110-180

Parts commonly replaced

  • Central heating flow NTC sensor
  • Wiring harness
  • Main circuit board (PCB)

Related codes

Full explanation for 118
501

Your boiler has tried to light several times but has failed to create a flame, meaning you currently have no heating or hot water.

High DIY-safe £100-350

What to check first

  1. Check if your home gas supply is active by testing another gas appliance like a hob.
  2. Verify that your gas prepaid meter (if applicable) has enough credit.
  3. If it is freezing outside, check that the white plastic condensate waste pipe is not frozen.
  4. Hold the 'Reset' button for five seconds to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Generator

Related codes

Full explanation for 501
502

Your boiler thinks it sees a flame even though the gas should be turned off, so it has shut down as a safety precaution.

High Engineer only £140-£350

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Main Control Board

Related codes

Full explanation for 502
Status & diagnostic codes

1 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

3P9 Diagnostic Your boiler is simply reminding you that its annual safety check and service are now due.
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