Lock out in Ideal mini combi gas boiler?

The boiler has not worked to its full potential for months e.g take ages to get hot water for bath and called plumber out for service and there was low gas pressure to boiler and he took valve out which had loads of grey dust or very fine metal shaving in the valve this was cleaned out and put back and tested and the hot water was great the heating seemed slightly less than before but next day it has gone into lock out and tried reset but it keeps locking out. Gas board put new mains pipe in our estate a few months ago and they have been called out and have seen the the debris in boiler but say its faulty/contaminated copper piping from meter to boiler which has only been in ten years and had no problem before.