i have a worcester 25si boiler and it was working fine until some builders took off 1 rads and then put it back on there are now only 5 that fully heat up and the rest just heat up a tiny bit or not at all and all rads have been bled
Something worth checking - have the builders opened up the valves on BOTH ends of the radiator , if not water won't be able to flow through - hence cold rads!