Good day everyone. Some very interesting reads on here regarding Nest, so thanks in advance for all those who have already posted. In short, our house is about 30 years old, we've been there about 8 years. About 4 or so years ago we fitted an OWL Intuition system which is still working well, I had high hopes that they would develop it a bit more and add more products to the range, but sadly that's not been the case and at the end of this month a new subscription cost comes in to play just to keep it running. Then I found Screwfix had a deal on a Nest so I grabbed one and that's the next project. The wiring for the OWL was pretty straightforward, it has its own hot water tank thermostat (that works in conjunction with the existing cylinder stat which is set higher, so OWL allows me to set different water temperatures for different times, although really we never use this feature much) I had a look at the wiring last night to refresh my memory, took notes and photos of exactly how everything is set up and my memory is now a little refreshed, mostly. (Thermostat in Lounge, boiler downstairs near kitchen, hot water tank, pump, 3-way valve and wiring block in upstairs airing cupboard, pretty standard I think) Attached is my scribble on wiring the Nest into the Y-Plan setup we have (I've also attached the previous OWL wiring diagram). Really, it's the wrong time of year for me to leave the family with no heating and hot water so I would really appreciate if anyone can take a look at my wiring plan and advise on it before I even think of swapping them over myself. Many thanks!