Ariston Boiler Fault Codes: Complete Error Code Guide
Ariston boiler fault codes help identify where a problem has occurred, such as the heating circuit, ignition system, temperature sensors, fan, PCB or condensate drainage system.
Common codes include 101 for overheating, 108 for insufficient water pressure, 501 for no flame detection and 612 for a fan-speed problem. Older Ariston boilers may use a different format, including A01, A77, E02, E04 and E34.
The meaning of a code can vary between Ariston boiler generations. Always confirm the code against the manual for your exact model before arranging a repair or ordering replacement parts.
Quick Answer
When an Ariston boiler detects unsafe or abnormal operating conditions, it may stop the burner and display a fault code.
You can sometimes try one reset using the boiler’s controls. However, recurring ignition, fan, gas, flue, electrical, condensate or overheating faults require investigation by a suitably qualified Gas Safe registered engineer.
Do not remove the boiler casing or replace a component based only on the displayed code.
How to Read Ariston Boiler Fault Codes
On many modern Ariston boilers, the first digit indicates the general area of the fault:
1: Central-heating circuit, circulation or temperature
2: Domestic hot-water circuit
3: Internal electronics or PCB
4: External controls or room sensors
5: Ignition and flame detection
6: Fan, air intake or flue system
7: Heating-zone controls
Ariston also separates faults that may clear when the cause disappears from lockouts that require a reset. If a code returns after resetting, there is normally an unresolved problem that needs professional diagnosis.
Older models, including some Microgenus boilers, use codes beginning with A or E. These should not be assumed to have the same meanings as codes on newer Clas, Genus, E-Combi or E-System boilers.
Common Ariston Boiler Fault Codes
| Fault Code | What it means | Safe action |
| 101 | Boiler overheating | Allow it to cool and reset once |
| 108 | Insufficient system water or low pressure | Check the pressure against the model manual |
| 501 | No flame detected | Check the property has gas and reset once |
| SP1 / 5P1 | First ignition attempt failed | Reset once |
| SP2 / 5P2 | Second ignition attempt failed | Arrange an engineer visit if repeated |
| SP3 / 5P3 | Flame cut-off or flame loss | Contact a Gas Safe engineer |
| 612 | Fan-speed error | Reset once and arrange testing if it returns |
| A01 | Ignition failure on selected older models | Check the gas supply and reset once |
| A77 | Condensate trap or sensor fault | Reset once and visually check the external pipe |
| E02 | Insufficient water pressure on selected older models | Check the pressure gauge |
| E04 | Domestic hot-water sensor open circuit on Microgenus II | Contact an engineer |
| E34 | Air-pressure switch fails to close when the fan runs | Contact a Gas Safe engineer |
Ariston 101 Fault Code: Overheating
The Ariston 101 fault code means the boiler has detected an overheat condition and shut down for safety.
This often happens when heated water cannot circulate away from the boiler correctly. Possible causes include a faulty circulation pump, trapped air, sludge, a blocked filter, restricted heat exchanger or faulty temperature sensor. Ariston identifies reduced water flow and temperature-sensor problems as common causes of 101.
Allow the boiler to cool and try one reset. If 101 returns, the pump, circulation route, heat exchanger and sensors should be professionally checked.
Internal link: Read our complete Ariston 101 fault code guide.
Ariston 501 Fault Code: No Flame Detected
The Ariston 501 fault code means the boiler attempted to ignite but could not establish or confirm a flame.
The problem may involve the gas supply, ignition electrode, flame-detection electrode, gas valve, burner, wiring or PCB.
A homeowner can check whether another gas appliance is working and whether a prepayment meter has credit. Try one reset only. If 501 returns, do not continue resetting the boiler.
Internal link: Read our full Ariston 501 error code guide.
Ariston SP1, SP2 and SP3 Fault Codes
These codes are officially displayed as 5P1, 5P2 and 5P3, although the number 5 may look like the letter S.
SP1 or 5P1 means the first ignition attempt was unsuccessful.
SP2 or 5P2 means the second ignition attempt failed.
SP3 or 5P3 means the flame was established but was then lost or detached.
SP3 should not be described simply as a third failed ignition attempt. Ariston places 5P1 and 5P2 under unsuccessful ignition attempts, while 5P3 relates to flame loss and possible ionisation problems.
Try one reset. Repeated codes require the gas supply, electrodes, gas valve, burner, combustion conditions and PCB to be tested.
Internal link: Read our Ariston SP1, SP2 and SP3 ignition-sequence guide.
Ariston 612 Fault Code: Fan-Speed Error
The Ariston 612 fault code means the fan is not operating at the speed expected by the boiler, or the controls are not receiving the correct fan-speed signal.
Possible causes include a slow or defective fan, a failed speed sensor, damaged wiring, poor electrical supply, a flue restriction or a PCB control fault. Ariston groups 612 with air-intake and flue-gas faults.
Try one reset. Do not remove the casing, touch the fan or inspect the internal flue connections yourself.
Internal link: Read our complete Ariston 612 fan fault guide.
Ariston A01 Fault Code: Ignition Failure
The Ariston A01 fault code is mainly found on older ranges, including selected Microgenus and Microgenus II boilers.
It means no flame was detected within the permitted ignition safety time. The Microgenus II manual describes A01 as no flame being detected after approximately seven seconds.
Check whether the property has a working gas supply and try one reset. If the boiler lights briefly and then displays A01, the flame may not be recognised correctly.
Possible causes include the ignition electrode, flame-detection electrode, spark generator, ignition lead, gas valve, electrical earth or PCB.
Internal link: Read our complete Ariston A01 fault code guide.
Ariston A77 Fault Code: Condensate Trap or Sensor
The Ariston A77 fault code is mainly associated with Microgenus HE boilers.
It can indicate:
A condensate trap full of water
A short-circuited condensate sensor
An open condensate-sensor circuit
A blocked or frozen external condensate pipe may stop water draining and contribute to the fault, but A77 does not automatically mean that the external pipe is frozen.
Try one reset and visually check only an easily accessible external condensate pipe. Do not remove or clean the internal trap yourself.
Internal link: Read our Ariston A77 condensate fault guide.
Other Modern Ariston Fault Codes
The following codes are worth including in this cornerstone guide, but they do not currently require separate long articles.
Ariston 103–107 and 1P1–1P3
These codes generally indicate insufficient water circulation.
The engineer may investigate the circulation pump, trapped air, filters, valves, system restrictions and flow or return temperatures. Ariston groups 103–107 and 1P1–1P3 with circulation problems.
Ariston 108 Fault Code
Error 108 indicates insufficient water in the heating circuit or low system pressure on compatible models.
Check the pressure shown on the display or gauge and follow the user manual. If the pressure repeatedly falls, the system may have a leak, expansion-vessel issue, pressure-relief valve problem or pressure-sensor fault.
Ariston 110 and 112 Fault Codes
These codes relate to central-heating temperature sensors or their circuits, depending on the exact model.
An engineer may need to test the flow or return thermistor, wiring and PCB connections. Do not order a thermistor until the exact model and sensor position have been confirmed.
Ariston 301–307 Fault Codes
Codes in the 300 group generally concern internal electronics.
Error 301 may indicate an EEPROM problem, 302 a communication problem, and 303 or 305–307 a PCB fault. Error 304 means the permitted number of resets has been exceeded, commonly more than five attempts within 15 minutes.
Stop resetting and arrange professional diagnosis.
Ariston 502 Fault Code
Code 502 means a flame has been detected while the gas valve should be closed.
This is a safety-related flame-detection fault. Do not continue resetting the boiler; contact a Gas Safe engineer.
Ariston 504 Fault Code
Error 504 indicates flame lift, flame detachment or loss of a stable flame.
Possible areas include gas pressure, ionisation, burner condition, combustion settings, flue operation and the flame-detection system.
Ariston 604 and 610 Fault Codes
Error 604 generally indicates insufficient fan speed on applicable boiler ranges.
Error 610 relates to an open thermofuse or thermal safety circuit. Both codes require professional investigation of combustion or safety components.
Older Ariston E-Series Fault Codes
The following meanings apply particularly to the Microgenus II range. Other Ariston models may assign different meanings, so the boiler manual must be checked.
Ariston E02 Fault Code
E02 means insufficient water pressure.
Check the pressure gauge. If the pressure remains low or continues falling after correction, contact an engineer to investigate the cause.
Ariston E04 and E05 Fault Codes
E04 means the domestic hot-water temperature probe is open circuit. E05 means the same sensor is short-circuited.
These faults may involve the NTC thermistor, wiring, connector or PCB. They are not homeowner repairs.
Ariston E06 to E09 Fault Codes
E06 and E07 relate to open- or short-circuit faults involving the central-heating flow sensor.
E08 and E09 relate to open- or short-circuit faults involving the return-temperature sensor.
Ariston E20 and E21 Fault Codes
E20 means a flame has been detected while the gas valve is closed.
E21 indicates an electrical connection problem, such as reversed live and neutral on the applicable Microgenus II range. A Gas Safe engineer or qualified electrician should investigate.
Ariston E33 and E34 Fault Codes
E33 means the air-pressure switch is already closed before the ignition sequence begins.
E34 means the air-pressure switch does not close when the fan runs. The engineer may inspect the fan, air-pressure switch, hoses, wiring, air intake and flue.
Ariston E99 Fault Code
E99 means the boiler has been reset too many times within a short period.
Stop resetting and arrange professional diagnosis. Repeated resets can hide the sequence of the original fault without correcting it.
What Can a Homeowner Check Safely?
The safe action depends on the displayed code and boiler model.
In general, a homeowner may:
- Record the complete fault code.
- Check whether the boiler has power.
- Check whether another gas appliance works when the fault concerns ignition.
- View the system-pressure gauge.
- Try one reset according to the user manual.
- Contact an engineer if the code returns.
Do not remove the casing, inspect internal wiring, clean electrodes, dismantle the condensate trap, touch the fan or adjust the gas valve.
Gas Safe Register states that anyone repairing, servicing or fitting a gas boiler must be Gas Safe registered and qualified for that work.
Finding the Correct Ariston Spare Part
Heating & Catering Parts supplies a wide selection of Ariston spare parts, including:
- Pumps and circulation components
- Thermistors and temperature sensors
- Ignition and flame-detection electrodes
- Fans
- Gas valves
- Heat exchangers
- Condensate components
- Wiring harnesses
- Printed circuit boards
A fault code identifies the affected system, but it does not always identify the failed part.
Before ordering, check the complete boiler model, GC number, manufacturer part number and the number printed on the existing component. Different production versions of the same boiler may use different parts.
What Can a Homeowner Check Safely?
The safe action depends on the displayed code and boiler model.
In general, a homeowner may:
- Record the complete fault code.
- Check whether the boiler has power.
- Check whether another gas appliance works when the fault concerns ignition.
- View the system-pressure gauge.
- Try one reset according to the user manual.
- Contact an engineer if the code returns.
Do not remove the casing, inspect internal wiring, clean electrodes, dismantle the condensate trap, touch the fan or adjust the gas valve.
Gas Safe Register states that anyone repairing, servicing or fitting a gas boiler must be Gas Safe registered and qualified for that work.
Finding the Correct Ariston Spare Part
Heating & Catering Parts supplies a wide selection of Ariston spare parts, including:
- Pumps and circulation components
- Thermistors and temperature sensors
- Ignition and flame-detection electrodes
- Fans
- Gas valves
- Heat exchangers
- Condensate components
- Wiring harnesses
- Printed circuit boards
A fault code identifies the affected system, but it does not always identify the failed part.
Before ordering, check the complete boiler model, GC number, manufacturer part number and the number printed on the existing component. Different production versions of the same boiler may use different parts.
What Can a Homeowner Check Safely?
The safe action depends on the displayed code and boiler model.
In general, a homeowner may:
Record the complete fault code.
Check whether the boiler has power.
Check whether another gas appliance works when the fault concerns ignition.
View the system-pressure gauge.
Try one reset according to the user manual.
Contact an engineer if the code returns.
Do not remove the casing, inspect internal wiring, clean electrodes, dismantle the condensate trap, touch the fan or adjust the gas valve.
Gas Safe Register states that anyone repairing, servicing or fitting a gas boiler must be Gas Safe registered and qualified for that work.
Finding the Correct Ariston Spare Part
Heating & Catering Parts supplies a wide selection of Ariston spare parts, including:
Pumps and circulation components
Thermistors and temperature sensors
Ignition and flame-detection electrodes
Fans
Gas valves
Heat exchangers
Condensate components
Wiring harnesses
Printed circuit boards
Frequently Asked Questions
You can try one reset using the instructions for your boiler. If the same fault returns, stop resetting and arrange professional diagnosis.
The reset clears the lockout, but it does not repair the underlying problem. A returning code indicates that the original fault remains.
No. Modern Clas, Genus and E-Combi boilers use different code formats from older Microgenus models. Always check the exact model manual.
No. Several components can produce similar symptoms. The part should be tested and its compatibility confirmed before replacement.
Internal boiler, gas, combustion, electrical safety and flue work should be completed by an appropriately qualified Gas Safe registered engineer.
Key Takeaways
- Ariston boiler fault codes identify problems like overheating, low water pressure, and no flame detected.
- Common codes include 101 for overheating, 108 for low pressure, and 501 for no flame; older models may use different formats.
- Always verify fault codes against the manual for your specific model before acting on them.
- Homeowners can perform basic checks like recording the fault code and viewing the pressure gauge but must contact a professional for complex issues.
- Gas Safe registered engineers should handle repairs related to gas, electrical, and combustion systems in Ariston boilers.
