I was unhappy leaving it so have left them with just the immersion heating the water. I'm waiting on a call from Telford technical to see if they can shed any light on it. No offence taken, I'm aware of the dangers of unvented cylinders and have wired many over the years and seen enough DIY...
its definitely a horizontal cylinder and has been installed correctly, as per instructions, although i didn't do the plumbing only being a lowly electrician. its a dual stat with an upper limit cut out combined. it has 2 probes out the back that sit inside the cylinder pocket.
Wiring up a system with 3 zones 1 for UFH 1 for Traditional rads 1 for HW first 2 work perfectly, Thermostat for HW will not operate when placed in cylinder pocket but clicks on and off when held. Any suggestions as to fault would be appreciated.