Three rads not working upstairs

[nightwalker.]

Hello I wonder if anyone can help, we have had some building work done and a new boiler and some new rads installled.
The boiler is a worcester 37cdi condensing. We have 7 radiators downstairs, 4 radiators on 1st floor and 1 radiator and towel rail on 2nd floor. All the radiators get hot, apart from 3 on 1st floor (2 bedroom, 1 Bathroom) The pipework to 1 bedroom and the bathroom is the original and as not been touched. The pipework to the other bedroom as been extended. Have switched off the radiators that get hot and only one of the three gets slightly warm not hot.
Have closed the valves and opened the air vent and re-opened the valves to check water flow,on each cold rad and it which seems ok.
Any advised would be helpful project has come to a standstill
thanking you