Hi i got a combi boiler(105e)how do i balance the system?radiator in loft only gets hot 3/4 hot bottom luke warm,been bled but no air,also got a towel rail in on suite in loft,that i have to bleed now and again as top of rail goes luke warm and then very hot when bled,have to top boiler up quite alot,top upto 1bar,but drops back to 0.5 bar after number of days??