High
Block 81 on Atag Q 25S

Your boiler has detected that a key safety sensor measuring exhaust gases has become unplugged, so it has safely shut itself down to prevent operation.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

The flue gas sensor is not connected although it was connected to the control. The burner is blocked until the flue gas sensor is reconnected.

From this model's manual
Verified against the Atag Q 25s installation & service manual, page 39.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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