Hi Short of getting someone in (at this stage), figured I'd see if anyone here can help so I at least know what to look for. I'm in a flat with an old gloworm micron 40ff, which according to online resources is a "conventional boiler", I also have an unvented cylinder. I'm a bit confused here because it's my understanding that an unvented cylinder gets it higher pressure from the cold supply coming in, but I'm also reading that conventional boilers need a cold water storage tank to feed them. So, is my unvented water supply at the pressure of the cold water tank feeding into the boiler? Surely the boiler would need to keep up with that pressure too which doesn't sound like something to expect from any type of boiler? am I totally misunderstanding how an unvented cylinder works? I'd like to put a nest thermostat in so trying to figure out what I should replace the boiler with to make sure everything will all work together.