BoilerFaultCodesAtag 85 Fault Code
The Atag 85 fault code means: your boiler is currently struggling to sense water moving through the system and has automatically started a short process to clear any trapped air before it attempts to fire up again.. It appears on 6 Atag models in our database.
Technical description: The control has not detected a water flow. The venting cycle is started. If during this cycle water flow is detected, the venting cycle is ended and the burner is released.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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 85: 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 85 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 85 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 7 July 2026