105 Low

Atag 105 Fault Code

The Atag 105 fault code means: your boiler has detected low water pressure and is automatically running a seven-minute process to remove trapped air from the system before it resumes normal operation.. It appears on 4 Atag models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: De-aeration program will start (if the pressure was below 0.7 bar). This will last for approx 7 mins.

DIY fix possible

Wait 7 minutes for the automatic de-aeration program to complete.Check the pressure gauge on the front of the boiler once the program has finished.If the pressure is below 1.0 bar, use the filling loop underneath the boiler to Top up the system to between 1.0 and 1.5 bar.

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Atag models that show the 105 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Atag 105 fault code information on this page is sourced and cross-checked against the official Atag service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026