104 High

Atag 104 Fault Code

The Atag 104 fault code means: your boiler has detected that water is not circulating correctly through the system, which prevents it from heating up safely.. It appears on 18 Atag models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Flow Check Failed
Typical repair cost £120-£350 (including labour)

DIY fix possible

Check that the boiler pressure gauge is between 1.0 and 1.5 barEnsure all radiator valves and isolation valves under the boiler are fully openBleed all radiators to remove trapped air bubbles from the pipeworkReset the boiler using the reset button once pressure is confirmed

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Atag models that show the 104 fault code

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

Source

Atag 104 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 31 August 2026