I just had a 210 Ltr "MAIN" unvented cylinder installed in my uncles house because i have always had one and they are brilliant, but its a total nightmare, the plumber who install it has the ticket to do it because he has repaired mine before, the problem goes alittle like this, pressure is fine, there have been two two port valves installed in sytem as required by manaul both operate fine when heat or hot water is called for, central heating works, fine no problems at all, open the cold taps and the water goes from cold to luke warm, open the hot tap and it goes from piping hot to freezing cold, the whole thing is not working at all, but outlet pipes at cylinder are hot, there is a toilet behind the cylinders current location with a sink and two seperate taps hot and cold, i.e. no mixer and the water misbehaves there as well, downstairs their are all mixer taps and the water just does not do what its supposed to do, what could it be.... ps plumber and electrician have been over the whole thing and they have no answer...