I have a sealed (combi) central heating system and am currently building an ensuite and wish to add to central heating system a towel rail. General advice appears to be to call in qualified plumber to drain down pressurized systems. Is this essential? Do I have to drain down entire system to fit new towel rail? Is it possible to shutdown all radiator valves and then simply cut in to a feed pipe to connect new towel rail? This latter option is appealing as feed pipe to existing bedroom radiator runs directly under where the new towel rail will go. Thanking you in advance of any replies.