Ariston Boiler Error Codes: A Complete Diagnostic and Troubleshooting Guide

Is your Ariston boiler displaying a numeric code, and you’ve lost hot water or heating? Don’t panic. Modern Ariston boilers (such as the Genus One, Clas One, Alteas, and Matis series) are equipped with advanced self-diagnostic systems that help identify issues quickly.

At Termix.ro, we have compiled this comprehensive guide to help you decode the most common Ariston error codes. Learn which issues you can fix yourself and when it’s time to call a certified gas engineer.

How to Read Ariston Error Codes

The first digit of the code usually indicates which system is affected:

  • 1xx – Primary Heating Circuit issues.

  • 2xx – Domestic Hot Water (DHW) Circuit issues.

  • 3xx – Internal PCB (Electronic Board) faults.

  • 4xx – External Communication errors.

  • 5xx – Ignition and Flame Detection problems.

  • 6xx – Air Intake or Flue Gas Discharge issues.

Most Common Ariston Errors & Quick Fixes

⚠️ Ariston Error 108 – Low Water Pressure

This is the most frequent issue. It means the system pressure has dropped below the minimum safety limit (usually 0.6 bar).

  • The Fix: Check the pressure gauge. If it is below 1 bar, use the filling loop (usually a small blue or black lever under the boiler) to top it up until it reaches 1.2 to 1.5 bar. Ensure the valve is tightly closed afterward.

⚠️ Ariston Error 501 – No Flame Detected

The boiler attempted to ignite but failed to detect a flame.

  • The Fix: First, check if your gas supply is turned on (check other gas appliances). Press the RESET button. If it happens repeatedly, the ignition electrode may be dirty or the gas valve may be faulty.

⚠️ Ariston Error 101 – Overheating

The safety limit thermostat has tripped because the water temperature is too high.

  • The Fix: Ensure your radiator valves are open and that there are no blockages in the system. Let the boiler cool down for 15 minutes, then press RESET.

⚠️ Ariston Error 304 – Too Many Resets

If the RESET button is pressed more than 5 times within 15 minutes, the boiler will lock out for safety.

  • The Fix: Turn the power off and back on at the fused spur, or wait 15 minutes for the lockout to clear automatically.

Quick Reference Table: Ariston Error Codes (One & Clas Series)

Error Code Meaning Recommended Action
103 - 107 Poor circulation Check pump or filter for blockages
110 Flow sensor fault Requires professional technician
201 DHW sensor fault Sensor replacement may be needed
303 PCB internal error Try Reset; if it persists, call service
504 Flame lift-out Check flue discharge and air intake
6P1 Air pressure switch delay Check fan and flue pipe for debris

1 01 Excessive temperature.
1 02 Short-circuit or disconnected pressure sensor.
1 03 1 04 1 05 1 06 1 07 Insufficient traffic.
1 08 Lack of water (filling required).
1 09 Installation pressure> 3 bar.
1 11 Lack of water (filling required).
1 10 Open circuit / Short circuit heating probe.
1 12 Open circuit / Short circuit heating return probe.
1 14 Open circuit / Short circuit external heating probe.
1 16 Open floor thermostat.
1 18 Primary circuit probe problem.
1 P1 1 P2 1 P3 Insufficient traffic signal.
1 P4 Lack of water (filling required).
1 P5 Incomplete filling.
1 P6 Incomplete filling.
1 P7 Too many fillings (> 5) in 50 minutes.
2 01 Open circuit / Short circuit probe w.
2 03 GENUS ONE SYSTEM open circuit boiler upper probe.
2 05 Open circuit acm probe (Solar kit optional).
2 09 GENUS ONE SYSTEM boiler overtemperature.
3 01 EEPROM error.
3 02 GU-GIU communication error.
3 03 Main board error.
3 04 Excessive no reset attempts (> 5) in 15 minutes.
3 05 Main board error.
3 06 Main board error.
3 07 Main board error.
3 13 Low Voltage Fault.
3 P9 Scheduled maintenance - call for technical assistance.

4 01 Electronic circuit problem.
4 07 Open circuit / Ambient probe short circuit (if present).
4 11 Camera sensor 1 unavailable.
4 12 Camera sensor 2 unavailable.
4 13 Camera sensor 3 unavailable.
5 01 No flame.
5 02 Detection of flame with gas valve closed.
5 03 Detection of flame with gas valve closed (After 20 seconds with 502).
5 04 Detachment of flame (After 6 times with 5P3).
5 P1 First ignition attempt failed.
5 P2 First ignition attempt failed.
5 P3 Detachment of flame.
5 P4 Detected 3 flame detachments in one cycle.
5 P5 Low gas pressure error.
5 P6 Ignition test failed.
6 04 Insufficient fan speed.
6 07 Approval of exhaust gas pressure switch before ignition.
6 08 Gas discharge pressure switch not approved (fan on).
6 P1 Approval delay for flue gas pressure switch.
6 P2 Opening the gas pressure switch during normal operation.
6 10 Thermal safety open.

6 11 Fan warning - Fault in the air inlet and / or exhaust pipes (Central shutdown, fan running for up to 20 minutes). If the problem is not resolved, error 612 appears.
6 12 Fan error.
701 Defective z1 turbo probe.
702 Defective turbo probe z2.
703 Defective turbo probe z3.
711 Defective z1 return probe.
712 Defective z2 return probe.
713 Defective z3 return probe.
722 Overtemperature zone 2.
723 Overtemperature zone 3.
750 Indefinite hydraulic diagram.
8 01 Calbration Tuning Fault.
8 02 Flame Sensed with Gas Valve Closed.
8 03 Mismatch kW size - parameter 229 (Mismatch kW size).
8 04 Decoupling clip-in required - see note (Decoupling Clip-In required).

When to Call a Professional?

While a homeowner can easily fix Error 108 (low pressure), any intervention involving the gas valve, the fan, the heat exchanger, or the internal electronics must be performed by a Gas Safe registered engineer.

Are you looking for Ariston spare parts or a new, high-efficiency heating system? The Termix team is here to provide top-tier equipment and technical support to keep your home warm and safe!