BoilerFaultCodesAtag Block 86 Fault Code
Also written as BLOCK86 — same fault.
The Atag Block 86 fault code means: your boiler has detected that the electricity supply coming from your wall socket is unstable or outside of the standard frequency range, preventing it from operating safely.. It appears on 3 Atag models in our database.
Technical description: The frequence of the power supply deviates more than 2,5Hz (<47,5Hz, >52,5Hz)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Atag models that show the Block 86 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag Block 86 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