Hi, I've got wet UF heating in part of my downstairs. It is split into 3 zones. The Heatmiser thermostats are wired to a Heatmiser wiring center. They are 3 wire stats - live, neutral and a volt free switched line. The boiler, pump and zone valves are managed from separate relays on the wiring centre. Original stats were Heatmiser PRTs. About a year ago 2 of the 3 died. They were replaced with Heatmiser Slimline stats (very similar). A few months back one of the replacement Slimline stats died and was replaced. A couple of weeks ago the same two died again. I now have another pair of warranty replacements, but I'm loath to install them without knowing what the issue was. Trouble shooting steps taken so far: Checked heating fuse - confirmed 3amp Checked and double checked everything is wired in correctly Run insulation test on the wiring for the effected stats - all seems fine Underfloor heating store (the supplier) think it is being caused by power surges. But I don't get it - why is it only effecting 2 of the 3 stats - the one on the other zone has been fine throughout. And anyway we have never had any issues with any of our other electrical kit. Any further thoughts would be much appreciated!