BoilerFaultCodesAtag Block 11 Fault Code
Also written as BLOCK11 — same fault.
The Atag Block 11 fault code means: your boiler has temporarily stopped heating your home because the water is not circulating fast enough to transfer heat away, likely due to a blockage in your pipes or radiators.. It appears on 4 Atag models in our database.
Technical description: Maximum ΔT of flow and return sensor in central heating has repeatedly been exceeded. During the block normal operation of the hot water supply is possible. The pump continues to operate at minimum capacity during the block.
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 11 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag Block 11 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