I want to alter pipework- 8mm- to replace old with new radiator upstairs . System has manifolds upstairs & down - under floors. Do I drain system as normal i.e. open drain cock at lowest point etc .Can I part drain ?. CH is about 20 yrs old. has both 8 & 10 mm pipework .
Also when hot water only is on , upstairs radiators get warm/hot.
Also when hot water only is on , upstairs radiators get warm/hot.