how to fix alpha cd 28c combi boiler neon B HELP?

brand new boiler, went to fire her up for the first time and it went through it's cycle, fan, pump ect ect and fired up, then 10secs later she locks out with neon b constantly illuminated, any ideas what it could be? the air vent is open so its not air trapped in the boiler, i've got a basic understanding of the guts of a boiler but no experience in fixing internal faults, thanks for any help :)