Ariston Boiler Error Codes: Causes & How to Fix Them

Last Updated on January 28, 2025

Ariston boilers are a popular choice for homeowners due to their efficiency and reliability. However, like any advanced appliance, they can occasionally encounter issues. Fortunately, Ariston boilers are equipped with error codes to help diagnose and fix problems quickly. 

In this guide, we’ll break down the most common Ariston boiler error codes, what they mean, and how to address them effectively.

Why Do Ariston Boilers Display Error Codes?

Error codes on Ariston boilers are designed to signal a fault within the system. These codes simplify the troubleshooting process by identifying the specific issue. Common reasons for error codes include:

• Faulty components
• Electrical or gas supply interruptions
• System blockages or leaks
• Incorrect settings

Understanding these codes is essential for resolving problems with your boiler promptly and avoiding costly repairs.

Common Ariston Boiler Error Codes and How to Fix Them

Below is a detailed overview of common Ariston boiler error codes, their potential causes, and recommended fixes:

1. Error Code 501: Ignition Failure

Cause:
This error occurs when the boiler fails to ignite the gas needed for heating or hot water. Common reasons include:

• An inactive gas supply (gas valve turned off or supply disruption).
• Faulty ignition electrodes or ignition leads.
• A defective gas valve or an issue with the gas pressure.
• Blockages in the burner or flue pipe.

Fix:

1. Gas Supply Check: Ensure the gas supply is active and the main valve is open. Contact your gas provider if there’s a supply issue.
2. Inspect Ignition Components: Inspect the ignition electrodes and wires for damage, dirt, or wear. Clean or replace them if necessary.
3. Boiler Reset: Press the reset button and monitor if the issue resolves.
4. Call a Gas Safe Engineer: If the problem persists, it could indicate deeper issues with the gas valve or burner that require professional assistance.

2. Error Code 108: Low Water Pressure

Cause:
Ariston boilers require a certain level of water pressure (typically around 1.5 bar) to function correctly. Low pressure may result from:

• Leaks in the system.
• Air trapped in radiators or pipes.
• Malfunctioning pressure sensors or valves.

Fix:

1. Check Pressure Gauge: Confirm that the pressure is below the recommended level.
2. Top Up the Pressure: Use the filling loop (often located under the boiler) to increase the pressure. Open the valves slowly until the gauge reaches 1.5 bar, then close them.
3. Inspect for Leaks: Look for visible leaks around the boiler, radiators, and pipes. If leaks are found, a Gas Safe registered engineer should repair them immediately.
4. Bleed Radiators: Air trapped in radiators can cause pressure drops. Use a radiator key to release the air, ensuring even heat distribution.

3. Error Code 103: High Water Temperature

Cause:
This code appears when the boiler’s water temperature exceeds safe operating limits. Causes include:

• A malfunctioning thermostat that fails to regulate temperature.
• A blocked or failing circulation pump leading to poor water circulation.
• A blocked heat exchanger means that the part of the boiler that transfers heat is clogged or obstructed. This prevents the hot water from flowing freely through the system, causing certain areas to overheat.

Fix:

1. Ensure Proper Circulation: Open all radiator valves to allow water to flow freely.
2. Bleed Radiators: Remove trapped air to improve circulation and prevent temperature spikes.
3. Inspect the Heat Exchanger: Limescale buildup in the heat exchanger can restrict flow and cause overheating. Descale the exchanger if necessary.
4. Call a Professional: A heating engineer should inspect the thermostat, pump, and heat exchanger if overheating persists.

4. Error Code 601: Fan Fault

Cause:
The boiler’s fan is vital for expelling harmful gases via the flue. A malfunctioning fan can result from:

• Electrical connection failures.
• Blockages in the fan blades or housing.
• A worn-out fan motor.

Fix:

1. Visual Inspection: Check the fan for dust, debris, or blockages. Clean the blades and housing carefully.
2. Verify Electrical Connections: Ensure all wires are securely connected to the fan motor.
3. Fan Replacement: If the fan motor is damaged or worn, a Gas Safe engineer should replace it.

5. Error Code 302: Flame Detection Error

Cause:
This error indicates that the boiler cannot detect a flame after ignition. Possible causes include:

• A malfunctioning flame sensor.
• Dirty electrodes preventing proper flame detection.
• Issues with gas supply or pressure.

Fix:

1. Gas Supply Check: Confirm that the gas supply is active and consistent.
2. Inspect the Flame Sensor: Clean the flame sensor with a soft cloth if it is dirty. Replace it if it appears damaged or worn.
3. Boiler Reset: Reset the boiler after performing the checks. If the issue remains unresolved, a professional heating engineer should investigate further.

6. Error Code 305: Flue Blockage Detected

Cause:
The flue pipe allows exhaust gases to escape safely. Blockages can occur due to:

• Debris, such as leaves or dirt, obstructing the flue.
• Ice buildup during cold weather.
• Flue misalignment or damage.

Fix:

1. Inspect the Flue Pipe: Remove any visible debris or obstructions.
2. Clear Ice: During winter, thaw any ice buildup around the flue using warm (not boiling) water.
3. Check Flue Alignment: Ensure the flue is correctly installed and securely connected.
4. Seek Professional Help: If the blockage persists, a qualified heating engineer can inspect and repair the flue system.

7. Error Code 104: Overheating

Cause:
Overheating is a safety feature triggered when the boiler’s temperature exceeds its threshold. Potential causes include:

• A failing circulation pump leading to stagnant water.
• A blocked heat exchanger trapping heat.
• Thermostat failure or incorrect calibration.

Fix:

1. Turn Off the Boiler: Allow the system to cool before performing any checks.
2. Inspect the Pump: Look for signs of wear or failure in the circulation pump. Replace it if necessary.
3. Descale the Heat Exchanger: Use a descaling solution to remove limescale and improve water flow.
4. Call a Technician: If overheating continues, the thermostat or other components may need repair or replacement.

How to Reset an Ariston Boiler

Resetting your Ariston boiler can resolve minor issues. Follow these steps:

1. Locate the reset button on your boiler (refer to the user manual for its exact location).
2. Press and hold the button for 5-10 seconds.
3. Wait for the boiler to reboot.
4. Check if the error code persists.

If the error code returns after resetting, it’s a sign of a more serious problem requiring professional attention.

Preventing Ariston Boiler Issues

Here are some tips to keep your boiler running smoothly:

1. Regular Servicing: Schedule an annual boiler service with a Gas Safe engineer.
2. Monitor Pressure Levels: Check the pressure gauge regularly and top up if needed.
3. Bleed Radiators: Remove trapped air to maintain efficient heating.
4. Clean Filters: Ensure filters are free from debris.
5. Protect the Flue: Keep the flue pipe clear of obstructions, especially during winter.

When to Call a Professional

While some Ariston boiler issues can be resolved at home, others require expert assistance. Contact a Gas Safe registered engineer if:

• The boiler repeatedly displays the same error code.
• There are unusual noises or smells coming from the boiler.
• The heating or hot water isn’t functioning despite troubleshooting.

Need a Reliable Boiler Replacement? Get a Free Quote Today!

If your Ariston boiler is showing frequent error codes or has reached the end of its lifespan, it might be time to consider a replacement. A new, energy-efficient boiler can save you money on energy bills, provide consistent heating, and give you peace of mind for years to come.

Getting a quote is quick and easy!
Simply fill out our online form, answer a few simple questions about your home and heating needs, and we’ll send you a personalised quote within minutes.

Don’t wait until your boiler breaks down completely—take the first step toward a warmer, more efficient home today.

Conclusion

Ariston boiler error codes are a helpful diagnostic tool for identifying and resolving issues quickly. By understanding these codes and their causes, you can perform basic troubleshooting and know when to seek professional help. 

Regular maintenance and prompt attention to faults will keep your boiler running efficiently, saving you time and money in the long run.

For more tips on boiler maintenance or to schedule a service, get in touch with a qualified heating engineer today!