How much does it cost to fix Atag error code Block 86?

Typical repair cost for the Atag Block 86 fault is £120-250 including labour.

Block 86 High

Atag Block 86 Fault Code

Q: What does the Atag Block 86 fault code mean?

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.

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)

Typical repair cost £120-250 (including labour)

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 27 April 2026