12 High

Atag 12 Fault Code

The Atag 12 fault code means: your boiler has encountered a deep internal communication problem within its computer control system and cannot operate.. It appears on 1 Atag model 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: Internal error
Typical repair cost £250-500 (including labour)

DIY fix possible

Locate the power switch or fused spur for the boilerTurn off the power for 60 secondsTurn the power back on and press the 'Reset' button

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Atag models that show the 12 fault code

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

Source

Atag 12 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