Hi all, Hoping someone here can help me. I have a brand new megaflo eco unvented indirect cylinder installed, I also have the nest learning thermostat and programmer fitted and wired in s plan (as per image attached below). The big question: when the nest thermostat calls for hot water it heats the water perfectly fine after approx 15-20min but if we are to use the water in the cylinder the water can stay cold for several hours after until the hotwater is again switched on via the nest thermostat. It would seem to me (with my simple mind) that the megaflo thermostat is not calling for hot water and only the nest thermostat calling for it as per the schedule setup or if we override the schedule and turn the hot water on? So to be clear if the nest thermostat is calling for hot water the water heats up within approx 15-20min. But if we say have 1-2 baths and empty the hot water from the cylinder the water does not then re-heat until the nest thermostat calls for hot water again. Here is the wiring diagram that has been used and physical wiring all looks to be in order. Any help will be greatly appreciated as currently I am at a loss as to why the cylinder's thermostat is not calling for heat on its own. Ps, cable from the nest terminal 3 is connected to cylinder thermostat terminal 1, and cylinder thermostat terminal 2 connected to hit water valve brown. Hope this all makes sense and thanks in advance.