What does the Biasi All operation lights OFF fault code mean?

Your boiler has no power and is completely unresponsive, meaning it cannot provide any heating or hot water.

How much does it cost to fix Biasi error code All operation lights OFF?

Typical repair cost for the Biasi All operation lights OFF fault is £90-280 including labour.

Check if the boiler's main power switch is turned on

Boiler does not start either in c.h. or d.h.w. mode. Fan still.

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

Work through these before the call-out.

Almost always a stuck diverter valve on combis.

Safety-critical — turn off, read this.