I have a Vaillant TURBOmax VUW 242/1E,or 282/1 E boiler system installed and I wish to drain the radiators to replace a rad and valves in the upstairs bathroom. Having studied the instruction manual I am a little unsure of the best procedure. I have no drains on any of the radiators and cant find any on the boiler. This is how the pipe work is assembled from left to right under boiler:- (pipe 1) central heating service valve, (pipe 2) unspecified "mains in?", (pipe 3) gas service valve, (pipe 4) cold water valve, (pipe 5) return central heating service valve, (pipe 6) Pressure relief valve. Any advice would be great and would also like advice on refilling the system. Thanks in advance.