Ariston Boiler Faults: Common Codes, Causes & Fixes

Common Ariston Boiler Faults

Most Ariston boiler faults display a specific error code. Some faults, such as low water pressure, may be resolved with a basic pressure adjustment. Gas, electrical and internal component faults should be diagnosed by a qualified engineer.

Low Water Pressure – Fault Code 108

Ariston fault code 108 indicates low water pressure. When the pressure falls too low, the boiler can lock out as a safety precaution.

Common signs include no heating or hot water, fault code 108 on the display, and a pressure gauge below 1 bar.

Possible causes include natural pressure loss, a small leak in the heating system, recent radiator bleeding, or recent plumbing work.

Check the pressure gauge first. If it is below the recommended level, the system may need repressurising. Many Ariston boilers have a filling loop underneath the boiler:

• Turn off the boiler.
• Locate the filling loop and valves.
• Slowly open the valves to let water into the system.
• Watch the pressure gauge and stop at around 1.5 bar.
• Close the valves and restart the boiler.

If the pressure keeps dropping, there may be a leak or another fault in the heating system. A qualified engineer should investigate the cause.

Ignition Failure – SP1 or SP2

An Ariston SP1 error or SP2 error indicates an ignition problem. The boiler cannot ignite correctly, so it may fail to provide heating or hot water.

Possible causes include faulty ignition leads, a blocked burner, gas supply problems, a faulty spark generator, debris affecting ignition, or faulty internal components.

Before arranging a repair, you can check the boiler pressure and thermostat settings. You can also check whether other gas appliances are working.

If the boiler continues to show SP1 or SP2, professional diagnosis is normally required. An engineer can inspect the ignition system and identify whether a component needs cleaning, repair or replacement.

No Flame Detected – Fault Code 501

Fault code 501 indicates that the boiler has not detected a flame. This can prevent the boiler from operating and leave you without heating or hot water.

Possible causes include thermocouple failure, gas valve problems, flue obstruction, or electrical faults.

Gas and combustion components should not be repaired as a DIY job. A qualified engineer needs to identify the cause before carrying out any repair.

PCB Faults – Fault Codes 301–307

The printed circuit board (PCB) controls many of the boiler's electronic components. Ariston fault codes 301 to 307 indicate PCB-related faults.

Signs can include multiple fault codes, controls not responding, intermittent operation, or complete system shutdown.

An engineer will normally check electrical connections and related components first. A loose connection may be straightforward to resolve, while water damage or PCB failure can require board replacement.

Fan Fault – Fault Code A41

The boiler fan helps remove combustion gases from the appliance. A fan fault can cause the boiler to lock out.

Possible causes include electrical supply problems, worn fan bearings, a blocked flue, or PCB communication problems.

Fan faults require professional diagnosis. An engineer can test the fan's electrical supply, inspect the fan and check related components before deciding whether replacement is required.

Air Pressure Switch Fault – Fault Code E43

The air pressure switch works with the fan and helps confirm that combustion gases can be safely removed. An E43 fault can prevent the boiler from operating.

The fault may be linked to the air pressure switch, fan, PCB or another part of the safety system. Because this involves the boiler's combustion and safety controls, professional diagnosis is required.

Other Ariston Boiler Error Codes

Ariston boilers can display a range of other fault codes depending on the model. The following gives a simplified guide to the codes covered on this page — not every code across every Ariston appliance.

Central Heating Circuit Errors

These codes relate to temperature, pressure and circulation within the heating system: 101 (overheating detected), 102 (pressure sensor fault), 103–107 (poor or insufficient water circulation), 108 (low water in the system), 109 (pressure too high), 110 (flow temperature probe fault), 112 (return temperature probe fault), 114 (external sensor issue), 116 (floor thermostat contact open), 118 (heating delivery probe fault), and 1P1–1P4 (circulation problems, depending on model).

Hot Water Circuit Errors

These codes relate to components associated with domestic hot water: 202 (storage temperature probe fault), 204 (solar collector probe fault), 205 (hot water probe open circuit), 207 (solar collector overheating), and 208 (solar collector frost protection).

PCB Errors

PCB-related codes can indicate communication or control-board faults: 301 (EEPROM error), 302 (communication error), 303/305/306/307 (PCB fault), 304 (too many resets in a short period), and 3P9 (service required).

Ignition and Flame Detection Errors

These codes relate to ignition and flame detection: 501 (no flame detected), 502 (flame detected when the gas valve was closed), 504 (flame lift), 5P1/5P3 (ignition failed — a related ignition-failure notation to SP1/SP2 above, shown differently depending on the display), and 5P4 (flame cut-off during operation).

Air, Flue and Gas Outlet Errors

These codes relate to the fan and safe movement of air and combustion gases: 604 (fan speed too low), 610 (thermofuse open), and 612 (incorrect fan speed reading).

Multi-Zone Heating Errors

For systems controlling multiple heating zones, codes can include 411/412/414 (room sensor circuit issues), 701/702/703 (defective send sensor), 711/712/713 (return sensor defective), 722/723 (overheating detected), and 750 (all heating zones locked).

The exact meaning of a fault code can vary between Ariston models, so check the boiler's manual where possible.

If You Smell Gas

Do not attempt to repair gas or combustion components yourself. If you smell gas at any point, stop immediately, do not operate light switches or naked flames, turn off the gas supply at the meter if it's safe to do so, ventilate the area, and call the National Gas Emergency Service on 0800 111 999 straight away.

When Should You Call a Professional?

You can sometimes resolve a low-pressure fault by repressurising the system. Most other Ariston boiler faults need professional attention.

A qualified heating engineer can diagnose electrical and gas-related faults, test internal boiler components, check safety systems, identify faulty parts, and carry out repairs safely.

If the boiler continues to lock out, displays a fault code repeatedly or shows signs of a more serious problem, arrange a professional inspection.

For Ariston faults that need professional attention, you can arrange a boiler repair in London with Serviceteam.

Is Your Ariston Boiler Worth Repairing?

Repeated breakdowns can be a sign that an older boiler is becoming less economical to repair.

Replacement may be worth considering if repair costs are becoming high, the boiler is over 10–12 years old, you are experiencing several faults each year, or replacement parts are becoming difficult to source.

The decision depends on the boiler's age, condition, repair cost and availability of parts.

Keeping Your Ariston Boiler Running Smoothly

Understanding common Ariston boiler faults can help you identify problems quickly. Low pressure may sometimes be resolved by repressurising the system, while ignition, PCB, fan and other internal faults generally require professional diagnosis.

Regular servicing can help identify potential problems before they lead to a breakdown. If your Ariston boiler is showing persistent fault codes or needs repeated repairs, an engineer can assess whether repair or replacement is the better option.

Need Help With an Ariston Boiler Fault?

Serviceteam can diagnose and repair boiler problems across London. If your boiler is showing a persistent fault code, contact us to arrange a repair.