BoilerFaultCodesAtag 109 Fault Code
The Atag 109 fault code means: your boiler has too much water inside it, which is causing the system pressure to rise above a safe operating level.. It appears on 18 Atag models in our database.
Technical description: Pressure >Pmax
DIY fix possible
Check that the internal or external filling loop valves are fully closed.Bleed water from a radiator using a radiator key to reduce the system pressure.Monitor the pressure gauge on the boiler until it returns to the green zone, typically between 1.0 and 1.5 bar.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like 109: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Atag models that show the 109 fault code
Click a model for the full fault code list and model-specific repair notes.
- i15R Repair: £80-220
- i15S Repair: £80-220
- i18R Repair: £80-220
- i18S Repair: £80-220
- i24C Repair: £80-220
- i24R Repair: £80-220
- i24S Repair: £80-220
- i28C Repair: £80-220
- i32R Repair: £80-220
- i32S Repair: £80-220
- i36C Repair: £80-220
- i40C Repair: £80-220
- i40R Repair: £80-220
- i40S Repair: £80-220
- iC Economiser 27 Plus Repair: £80-220
- iC Economiser 35 Plus Repair: £80-220
- iC Economiser 39 Plus Repair: £80-220
- iC Range Repair: £80-220
Source
Atag 109 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