Replaced radiators on a worcester boiler now heating is not working??

We are updating my late fathers house and a plumber turned off the heating to take off a radiator to plaster the walls, we are no longer using the project manager as they shafted us!! So we have put the radiators all back on and have filled them and checked for leaks etc, but we can not get the heating to work. The hot water is working fine, its on a worcester combi boiler with no thermostate so we feel a bit stumped, should we just find a new plumber?