workhard - the existing system in the house I moved to a year & a half ago was the same as yours: vent into c/w tank, vent into c/h header tank, hot water cylinder ... but connected to an oil fired jobby, oh, and no controls to speak of. The installers obviously added zone valves (3 of them), converted the system into 'semi-pressurised' by adding a valve to the end of the c/h expansion pipe in the attic plus an expansion vessel plus a by-pass valve.
Before they did all this they flushed out, inspected all the pipework (easy access as the house was empty so floorboards could be lifted) and pressure tested it. It'll be clear to most of the guys here that this aspect of the install should be taken as read by any decent installer but workhard I'd advise talking about these 'preliminaries' with your guy in advance.
Before they did all this they flushed out, inspected all the pipework (easy access as the house was empty so floorboards could be lifted) and pressure tested it. It'll be clear to most of the guys here that this aspect of the install should be taken as read by any decent installer but workhard I'd advise talking about these 'preliminaries' with your guy in advance.