Had a vaillant ecotec plus 615 fitted recently only for economy reasons. As the system ran well on the old classic balanced flue unit,this was a vented system.All good with new sealed system except the bathroom vertical rad (1800 x 200 12 tubes @ 25 o/d) will barely warm up. Shut every thing off and it heats up, bled it, open other rads and it stays cool. Both flow and return are hot at valves,lock shield wide open and TRV at max. It will warm accross the bottom and sometimes start warming up 3rd tube in and then a little at top at front, the back stays cold. It,s a micro bore system that was hot flushed ( not pressure) and mangaclean fitted,installers seem clueless,it think it,s restricted flow,any ideas. Thanks