Ariston Boiler Error Codes Causes & Fixes

If your Ariston boiler is flashing an error code, you’re not alone—many UK homeowners and landlords experience boiler problems, especially as systems age or head into winter.

This guide is designed to offer practical, step-by-step advice for resolving common issues with Ariston boilers found in UK homes, including the Clas, Genus, and E-Combi models. Note that error codes can vary slightly between models, so checking your boiler manual for specifics is wise.

What Are Common Ariston Boiler Problems and Why Do Error Codes Appear?

Modern Ariston boilers use built-in sensors and control boards to monitor the system. If a component stops working correctly or a parameter falls outside normal limits, the boiler may shut down for safety and display a fault code on the screen. These error codes help pinpoint the source of the fault, allowing for faster and safer repairs.

Common triggers include low water pressure, ignition faults, sensor failures, or circulation blockages. Error codes offer essential information—but some issues can be safely addressed by homeowners, while others must be left to Gas Safe registered engineers.

Typical Ariston Fault Codes and Their Meanings

Here’s a breakdown of common fault codes on Ariston boilers, with a focus on the Clas, Genus, and E-Combi ranges. Remember, not every code appears on every model, and some meanings vary by generation.

1xx Series – Heating and Pressure Issues

• 101: Overheating detected. The boiler senses water temperature rising too high, usually due to poor circulation, pump problems, or excessive scaling. Shut off and allow the boiler to cool, then seek professional advice if the issue returns.
• 102: Pressure sensor error. The sensor can’t read system pressure correctly—may be a failing sensor or wiring issue. Requires engineer inspection.
• 103, 104, 105, 106, 107: Water circulation problems—possible causes are insufficient water, blockages, trapped air, or a stuck pump. The boiler will lock out to prevent damage.
• 108: Low water pressure. If the display shows code 108, the pressure is below safe minimum, typically under 1.0 bar. You can often top this up yourself—see instructions below.

3xx Series – PCB, EEPROM, and Communication Faults

• 301–304: PCB or EEPROM memory errors. These indicate issues with the boiler’s internal memory or control logic and require professional diagnosis.
• 305, 306, 307: PCB communication errors. Data transfer faults or intermittent signals between the main PCB and sensors. These are not homeowner repairable and need a Gas Safe engineer to inspect, test, and possibly replace the PCB.

5xx Series – Ignition, Flame, and Supply Issues

• 501: Boiler failed to detect a flame after ignition—could be due to blocked jets, faulty ignition leads or electrode, or a gas supply issue. Professional intervention required.
• 5P1, 5P2: Ignition attempts have failed multiple times. Indicates a significant fault somewhere in the gas, ignition, or flue system. Shut down and call an engineer.

6xx Series – Flue, Fan, and Air Pressure

• 607: Fan error—either not running or running at incorrect speed. Since the fan extracts combustion gases, it’s a safety risk and must be checked by a professional.
• 6P1, 6P2: Air pressure switch faults. These prevent operation if air or exhaust flow is not as designed—usually caused by a blocked or iced flue or faulty switch.

7xx Series – Multi-Zone Heating and Sensor Faults

• 7xx (700+): Multi-zone sensor errors—faults with temperature sensors, or circuit issues in multi-zone systems. These may cause persistent lockouts and typically need an engineer to resolve.

DIY Troubleshooting Tips for Common Boiler Issues

You can fix some minor faults on your Ariston boiler safely at home. For anything involving gas, PCB, or internal parts, always call a Gas Safe registered engineer.

How to Safely Re-Pressurise an Ariston Boiler (Code 108)

1. Find the filling loop: Look for the silver braided hose under your boiler.
2. Open valves slowly: Turn each valve gently, one at a time, watching the pressure gauge rise. Avoid opening them suddenly to prevent leaks.
3. Monitor pressure: Bring the pressure up gradually to 1.0–1.5 bar (system cold).
4. Close valves firmly: Once pressure is correct, close both ends securely. Do not overtighten.
5. Check for drips: Wipe connections and check for any signs of leaking water.

If you notice rapid or repeated pressure loss, you may have a leak. Urgently switch off the boiler and call an engineer.

Frozen Condensate Pipe

If your Ariston boiler stops in winter and shows a “no ignition” error or the pipe outside is covered in frost, a frozen condensate pipe could be the cause.

• Pour warm (not boiling) water along the outside pipe until thawed.
• Insulate the pipe to prevent future freezing.
• Always reset the boiler after clearing the fault (see below).

Thermostat and TRV Check

If you have no heating, double-check your wall thermostat and any radiator valves are set above current room temperature, and make sure thermostat batteries aren’t flat.

How to Safely Reset Your Ariston Boiler

After correcting a minor fault (like topping up pressure or thawing a pipe):

1. Press the reset button (see control panel, often marked ‘reset’ or a circular arrow).
2. Release and wait: The boiler should restart; give it 60 seconds.
3. Monitor operation: If the same code reappears immediately, do not repeatedly reset—seek professional help.

Never reset the boiler more than once without resolving the fault.

When to Call a Gas Safe Registered Engineer

Do not attempt repairs on the gas supply, PCB, or internal wiring. Professional help is required for:

• PCB and communication errors (301–307)
• Gas supply, ignition, or flame detection (501, 5P1, 5P2)
• Fan and air pressure faults (607, 6P1, 6P2)
• Persistent overheating or sensor errors (101, 102, 700 series)
• Visible leaks from the boiler or repeated pressure drops
• Suspected gas smells or CO alarm activation

Gas safety law in the UK requires all boiler gas work to be carried out by a qualified Gas Safe registered engineer. Refer to the Gas Safe Register to find an accredited local specialist.

Preventative Maintenance Tips

• Annual servicing: Arrange a yearly full service with a Gas Safe engineer to keep your warranty and home insurance valid.
• Regular checks: Monitor pressure and bleed radiators at least two to three times a year.
• Insulate pipes: Protect external condensate pipes with proper insulation.
• Keep vents clear: Ensure nothing blocks air intakes or flues.

Regular care helps reduce breakdowns and lowers running costs.

Typical Repair Costs and Insurance

• Pressure sensor or low-pressure fixes: £100–£200
• Ignition or electrode faults: £120–£250
• PCB or major electronic part replacement: £300–£450+
• Fan or air pressure switch replacement: £175–£350

Home emergency insurance sometimes covers boiler repairs, but read policies carefully. Most require boilers to be under a certain age and serviced annually.

FAQ Section

What do Ariston boiler error codes mean?

An error code points to a specific problem—anything from low pressure (108), overheating (101), to ignition or PCB faults. They help you or your engineer pinpoint what’s gone wrong.

Can I fix boiler error codes myself?

Some minor issues—like low pressure or topping up water—can be safely resolved if you follow the instructions. Repeated pressure drops, leaks, internal faults, or any gas issues must be handled by a Gas Safe engineer.

How do I reset my Ariston boiler?

Press the ‘reset’ button on the front panel, then wait up to 60 seconds for normal operation. If a fault code returns, do not continue resetting—call a professional.

What should I do if my boiler loses pressure often?

Frequent pressure loss suggests a leak. Stop using the boiler and call a Gas Safe engineer. Top-ups should only be occasional.

When is it legally required to call a Gas Safe engineer?

If any repair touches the gas supply, PCB, internal wiring, combustion/air system, or if you smell gas or suspect a CO leak, legally only a Gas Safe registered professional can work on it.

How much does a typical Ariston boiler repair cost?

Depending on the fault, expect £100–£450. The most expensive are PCB or major component replacements.

Is a yearly boiler service important?

Yes. It keeps your warranty valid, is often required for insurance, and is critical for safety and efficiency.

Are faults covered by home insurance?

Some policies have home emergency cover for boilers under a set age and only if serviced annually. Always check the small print and service your boiler every year.

Where can I find professional help for Ariston boiler codes?

Use the Gas Safe Register to find a local engineer, or contact reputable suppliers like Boilers2Go for guidance on repairs and new boilers.