Ariston Boiler Faults: Common Problems & Solutions

Top 6 Ariston Boiler Faults You're Likely to Encounter

Most Ariston boiler faults display specific error codes on your boiler's interface, making it easier to identify the problem. You can fix a few errors yourself, but when it gets complicated, it's best to bring in a gas heating registered engineer for a professional boiler repair service.

1. Low Water Pressure (Fault Code 108)

The Ariston boiler fault code 108 indicates low water pressure, one of the most common issues affecting these systems. When pressure drops too low, your boiler will automatically lock out as a safety precaution.

Symptoms:

• No heating or hot water
• Fault code 108 displayed
• Pressure gauge needle below 1 bar

Causes:

• Natural pressure loss over time
• Small leaks in the system
• Radiator bleeding
• Recent plumbing work

How to Fix Low Water Pressure:
Check your boiler's pressure gauge first. If the needle sits below 1 bar, you'll need to repressurise the system.

Most Ariston boilers have a filling loop underneath the unit.

1. Turn off your boiler
2. Locate the filling loop (usually two braided hoses with valves)
3. Slowly open both valves to allow water into the system
4. Watch the pressure gauge and stop when it reaches 1.5 bar
5. Close both valves and restart your boiler

If pressure drops repeatedly, you likely have a leak somewhere in your heating system. Contact a Gas Safe engineer to locate and repair the leak.

2. Ignition Failure (Fault Codes SP1 or SP2)

When your Ariston boiler fails to ignite, it will display either SP1 or SP2 fault codes. This problem prevents your boiler from firing up to provide heating or hot water.

Common Causes:

• Faulty ignition leads
• Blocked burner
• Gas supply issues
• Faulty spark generator
• Debris in the pilot jet
• Broken diaphragms

How to Address Ignition Problems:
Start by checking your boiler pressure and thermostat settings. Ensure your gas supply is working by testing other gas appliances.

However, ignition faults typically require professional diagnosis. A Gas Safe engineer can safely inspect the ignition system, clean blocked components, or replace faulty parts.

3. No Pilot Light (Fault Code 501)

The pilot light is responsible for lighting the main burner when the boiler starts running. When this fails, you'll see fault code 501 and lose all heating and hot water.

Potential Causes:

• Thermocouple failure
• Gas valve blockage
• Flue obstruction
• Electrical faults

Professional Repair Required:
Pilot light issues involve gas components and safety systems, making them unsuitable for DIY repair. A qualified engineer must diagnose whether the thermocouple, gas valve, or another component needs replacement.

4. PCB Faults (Fault Codes 301-307)

The Printed Circuit Board (PCB) acts as your boiler's control centre, coordinating all electronic components. Ariston boiler fault codes 301 through 307 indicate various PCB faults.

Signs of PCB Issues:

• Multiple fault codes are appearing
• The boiler is not responding to the controls
• Intermittent operation
• Complete system shutdown

Repair Options:
PCB problems range from loose connections to complete board failure. An engineer will test electrical connections first, as this is often a quick fix. However, water damage or component failure may require PCB replacement, which can be costly on older boilers.

5. Fan Fault (Fault Code A41)

Your boiler's fan removes dangerous exhaust gases from your home. The A41 fault code indicates the fan isn't operating correctly, causing the boiler to lock out for safety.

Why Fan Faults Occur:

• Electrical supply problems
• Worn bearings
• Blocked flue
• PCB communication issues

Professional Diagnosis Essential:
Fan repairs require Gas Safe expertise due to safety implications. Engineers will test the electrical supply to the fan and inspect for physical damage. Fan replacement is common, especially in older boilers where wear and tear have taken their toll.

6. Air Pressure Switch Fault (Fault Code E43)

The air pressure switch works with the fan to ensure safe gas extraction. When faulty, your boiler displays error code E43 and won't operate.

Safety Implications:
This fault prevents your boiler from safely removing combustion gases, making it dangerous to use. The boiler locks out automatically to protect your household from carbon monoxide exposure.

Professional Repair Required:
Air pressure switch problems often connect to PCB or fan issues. Engineers will test the entire safety chain to identify whether the switch itself needs replacement or if related components are causing the fault.

Other Ariston Boiler Error Codes – Explained Simply

Boilers often display error codes to help identify what's gone wrong. Below is a simplified guide to the most common Ariston error codes, grouped by system area, so you can understand what they mean and why they appear.

Central Heating Circuit Errors

These errors usually point to issues with temperature, water pressure, or circulation inside the heating system.

Hot Water Circuit Errors

These codes focus on the parts of your boiler that heat domestic hot water.

Internal PCB (Printed Circuit Board) Errors

The PCB is the "brain" of the boiler. Errors here are often serious and may require an engineer's attention.

External PCB Errors

407 – Room sensor circuit fault

Ignition & Detection Issues

These relate to flame detection and gas ignition.

Air / Flue / Gas Outlet Errors

These involve the safe movement of air and gases through the system.

Multi-Zone Heating Errors

For systems controlling multiple heating zones.

✅ What This Means for You

• Minor issues like low water pressure (code 108) can sometimes be solved by topping up your boiler.
• More complex faults, especially PCB or ignition errors, need a gas safe registered engineer.
• Error codes are your boiler's way of protecting itself and your home; never ignore them.

When Should You Call a Professional?

While you can safely repressurise your boiler system yourself, most other Ariston boiler faults require professional attention.

Gas heating engineers have the expertise and tools to:

• Safely diagnose electrical and gas-related faults
• Access internal boiler components
• Test safety systems properly
• Provide warranties on repair work

Attempting DIY repairs on gas appliances is dangerous and illegal. Always contact a qualified professional for anything beyond basic pressure adjustments.

Is Your Boiler Worth Repairing?

Frequent breakdowns often indicate your boiler is reaching the end of its useful life. Consider replacement if:

• Repair costs exceed 50% of a new boiler's price
• Your boiler is over 10-12 years old
• You're experiencing multiple faults annually
• Replacement parts are becoming difficult to source

Modern boilers offer improved efficiency, reliability, and warranties that can provide better long-term value than continued repairs.

Keep Your Heating System Running Smoothly

Understanding common Ariston boiler faults helps you respond quickly when problems occur. While some issues like low pressure have simple solutions, most fault codes require professional diagnosis and repair.

Regular boiler servicing can prevent many common problems and identify potential issues before boiler breakdowns. If your boiler is displaying persistent fault codes or requiring frequent repairs, it might be time to consider a replacement system.

For immediate assistance with Ariston boiler problems, contact our heating professionals who can safely diagnose and repair your heating system, ensuring your home stays warm and comfortable.