ta chris but without sounding like a **** what is a unvented system..i do not have a combi,and the system is belived to be gravity feed into the taps this i understand i think.as for the flexi pipe it is only 10-15 mm but does not apper to affect the water flow into the bath even though it has...
i was told i could use a flexible fitting for my bath connections,,,a bit like speed fit...however these are white and nylon wrapped.
I have connected one end to the bath taps and the other to a 22mm copper pipe compression fit using the nut and olive which was supplied.Their are no leaks but...