We have had a new boiler fitted into our home. We have had the system changed from a back boiler/ tank system to a condensing boiler. We have had some issue's with the installer about power flushing the sytem. He has not done one as he said it does not need doing. Can somebody please tell me if this is correct. Is it a costly job to do? Also where the flue comes out of the wall (we have had boiler fitted into the loft) does this need a grommet or some sort of covering. It looks a tight fit from ground level but am concerned about water ingress. Many thanks.