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Last updated: 7th May, 2024


ATAG Boiler Error Codes - How To Fix

ATAG Boiler Error Codes - How To Fix

Key takeaways

  • Error codes facilitate the identification of boiler issues.
  • Some errors can be resolved by the homeowner, while others require professional assistance.
  • Safety must be prioritised when addressing boiler malfunctions.

When an ATAG boiler displays an error code, the meaning behind each code provides insight into the nature of the problem.

Understanding and troubleshooting ATAG boiler error codes is essential for maintaining the efficient operation of your heating system. Modern boilers are equipped with diagnostic systems that can alert you to a range of issues through specific error codes. 

This ability to self-diagnose simplifies the process of pinpointing malfunctions, which can vary from low system pressure to sensor faults. Homeowners can often resolve some of these issues without the need for professional help, saving time and money.

When an ATAG boiler displays an error code, the meaning behind each code provides insight into the nature of the problem. For example, error code 40 often indicates an issue with the boiler's fan, while code 111 may signal an overheat situation that has caused the unit to lock out for safety reasons. 

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Error code 101 usually pertains to a problem with the ignition system. Each code prompts a different response, ranging from simple resets to component checks or replacements. However, it is essential to approach these errors with caution, adhering to safety guidelines and consulting with a qualified technician when necessary.

Understanding ATAG Boiler Error Codes

When an ATAG boiler encounters an issue, it conveys this through specific error codes displayed on the control panel. These codes are essential for a homeowner or technician to diagnose and resolve faults.

Remember it is ALWAYS a good idea to call a Gas Safe engineer to assess and fix any boiler issue!

ATAG Boiler Error Code 10

Error Code: 10

Description: Outside Sensor Error

Issue: Indicates a problem with the outside sensor in the heating or HVAC system, typically responsible for measuring outdoor temperature or environmental conditions.


Turn off the heating  system.

Check the wiring and connections of the outside sensor, usually located outside the home.

If necessary, contact a qualified Gas Safe engineer for diagnosis and repair.

ATAG Boiler Error Code 20

For error code 20, the primary cause noted is a 'Flow sensor error'. This technical reading signifies that:

  • The flow sensor, which governs the measurement of fluid rate within the system, may be malfunctioning.

  • It can point towards either a sensor failure or an issue within the flow system that needs to be addressed.

ATAG Boiler Error Code 40

ATAG boiler error code 40 signals a malfunction with the return sensor, which monitors the temperature of water re-entering the boiler. This issue necessitates a prompt and careful resolution.

ATAG Boiler Error Code 61

The error code 61 indicates an issue with the flow sensor. The flow sensor tracks the temperature of water exiting the boiler; a malfunction can cause heating disruptions. Checking connections or replacing the sensor may resolve this error.

ATAG Boiler Error Code 78

For error code 78, a professional heating engineer should be consulted. The code pertains to a fault in the outside sensor or linking cables, which measure external temperatures to optimise heating efficiency.

ATAG Boiler Error Code 105

When confronted with error code 105, the focus should be on the boiler's condensing process. The condensing pipe may be blocked or frozen, calling for cleaning or thawing as necessary to maintain boiler performance.

ATAG Boiler Error Code 110

Error code 110 presents a high water pressure problem. Pressure too high in your system can pose a safety risk. Reducing the pressure by bleeding radiators or consulting a qualified installer for maintenance is advisable.

ATAG Boiler Error Code 111

When encountering the ATAG boiler error code 111, it indicates an issue with the appliance's ignition. The boiler's inability to light may be due to several factors such as the gas valve, supply, or burner.

ATAG Boiler Error Code 119

Error code 119 usually reflects a fault with the fan's operation. This component is essential for ensuring harmful gases are safely expelled and for drawing in fresh air necessary for combustion. If the boiler displays this error:

  • Check the fan assembly: Ensure it is free from obstructions and operational.

  • Examine electrical connections: Loose wiring may affect the fan's performance.

ATAG Boiler Error Code 129

The appearance of error code 129 often signals an issue with the flow sensor or the return sensor within the central heating system. These sensors monitor the temperature of water entering and exiting the boiler:

  • Inspect the flow sensor: Look for signs of damage or failure and consider replacement if needed.

  • Return sensor check: Similar to the flow sensor, this sensor must be intact and properly connected.

ATAG Boiler Error Code 133

Code 133 on an ATAG boiler generally points to an anomaly with the gas supply. Trouble with the gas can stem from several areas:

  • Verify gas supply: Confirm that the boiler's gas valve is open and the supply is consistent.

  • Gas valve assessment: An improper functioning Honeywell electric valve might need professional attention.

  • Burner inspection: An obstructed burner could also disrupt the gas delivery or ignition.

ATAG Boiler Error Code 151

This error denotes a potential fault with the hot water facility's sensor, which could stem from various causes:

  • Sensor evaluation: Ensure the hot water sensor is connected properly and functioning.

  • System balance: Evaluate whether components like the Caleffi SATK30 are influencing the sensor's readings and adjust accordingly.

Problems associated with these error codes may compromise both the central heating and hot water supply of the residence. Consultation with a certified technician is recommended to resolve these issues safely and effectively.

ATAG Boiler Error Code 101

ATAG boiler error codes signal to the user that there is a specific issue requiring attention. Error code 101 generally indicates a problem with the ignition sequence, potentially involving the thermostat or gas supply, which may lead to the boiler failing to start.

ATAG Boiler Error Code 102

Error code 102 typically signifies a fault with the boiler's fan or flue. The user should check for obstructions in the flue and ensure the fan is functioning correctly.

ATAG Boiler Error Code 104

If a user encounters error code 104, it suggests an issue with the water pressure in the heating system. One should verify the pressure gauge and, if necessary, adjust the pressure to fall within the standard range of 1-2 bar.

ATAG Boiler Error Code 108

The appearance of error code 108 often points to a problem with the thermostat connection. Users are advised to inspect the wiring and connections of the thermostat to ensure they're intact and correctly configured.

ATAG Boiler Error Code 1P4

Unusual error code 1P4 relates to internal communication errors within the boiler's circuitry. This situation may require professional assessment to identify and resolve any electronic faults.

ATAG Boiler Error Code 109

Error code 109 is commonly associated with a low system pressure warning. It is usually rectified by repressurising the system. The boiler manual provides guidance on how to safely do this.

ATAG Boiler Error Code 501

An ATAG boiler displaying error code 501 is indicating a sensor fault. Check sensor connections and if the fault persists, the sensor might need replacing, often necessitating an engineer's expertise.

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Frequently Asked Questions

How do you reset the boiler an ATAG Boiler?

To reset an ATAG boiler, one typically needs to locate the reset button on the boiler's display panel. After pressing and holding this button for a few seconds, the boiler should reset, clearing any minor errors and resuming normal operation.

Why is the spanner flashing on my ATAG boiler?

A flashing spanner on an ATAG boiler's display often indicates a fault that requires attention. It may be a signal that the boiler is operating in service mode. It's advisable to consult the user manual or contact a certified engineer for detailed diagnostics.

What are the ATAG boiler fault codes?

ATAG boiler fault codes are alphanumeric indicators displayed on the boiler to diagnose specific issues. These codes often point towards the nature of the problem within the boiler system, such as fault code 118 suggesting low system pressure or codes related to fan errors.

How do I clear the error code on my ATAG boiler?

To clear an error code on an ATAG boiler, first, address the underlying problem indicated by the code. Once the issue is resolved, the error code can be cleared by resetting the boiler, which is typically done by holding down the reset button as per the manufacturer's instructions.

What does F1 and a spanner mean on a boiler?

The appearance of an F1 error code, alongside a spanner symbol on a boiler, often denotes a specific fault or maintenance requirement. While the exact meaning may vary by make and model, it generally signals an issue that may need professional attention.

How is service mode or blocking activated on an ATAG boiler for maintenance purposes?

Service mode or blocking is activated on an ATAG boiler to allow safe maintenance or diagnostics to be performed. This is usually initiated by a qualified engineer who can access the service settings by entering a specific sequence of commands on the boiler's control panel.

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.