High
L3 on Biasi Concept 400 20 1 Mfs

Your boiler has detected that hot water is not circulating properly around your radiators, meaning your heating system cannot function correctly.

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

External pump / C.h. circuit - check External pump, C.h. circuit, C.h. flow/return temp. probe NTC

From this model's manual
Verified against the Biasi Bm Biasi Concept 400 20 1 Mfs installation & service manual.
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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