Well well, what a helpful bunch of sarcastic idiots you all are, eh? Maybe you should all just give up wasting your time answering threads on a forum, cos it ain't helping!!
The bypass... sorry did I not mention I have 2 heat leak pipes connecting flow and return!
But... for the record, yes I installed the unvented cylinder, been operating 100% for 8 years now! In fact, I'd had done the boiler too but it needed a building regs certificate so had to get a 'jobbing' plumber in to do it... and I painfully watched him do all I could do, and made a right hash of it – sloppy, pipes not straight, sealant all over the Tiger Loop, scratched the vessel to heck, and get this, didn't even tighten the 10mm nuts around the fire valve which I discovered after 4 days and the smell of oil!! So don't tell me to get professionals in, I've been bitten by this many times now, fed up with so called 'pros' on 5 or 6 occasions with other building work!
So yes, I choose to do the work myself, ok so I've clearly missed something here with the heat loss, hands up, but having replumbed an entire 3 story, 3000sq ft Victorian home, replacing all copper for PVC, zoning it, laying the UFH and not a single leak when pressure tested to 4.5bar, I think a tiny pat on the back would be welcome! Not to mention rewiring half the house, tiling 3 en suites and main bathroom, designing & installing the kitchen, laying carpets, taking the staircase apart to dip it to bare wood and rebuild it, removing the entire ground floor boards and joists, flip I could go on all day – so don't make me sound like a F*****g idiot!!!!
Thanks for all your help, it's been eventful...
As the regulations grow , the protectionism follows
and I doubt it was PVC you used too.