(Sorry for all those diving in here hoping its an example of one blowing up!). I've been reading alot on here about unvented cylinders and their risk of explosion (since I had to fix a faulty thermostat in situe on a Megaflo and had serious paranoia - needless to say, although working fine it'll be replaced in days). I totally agree all round on the safety features that UV has, and to be frank I think those harping on about explosions are being dramatic in the extreme. For example in this case if the thermostat overheats, then the safety will cut in, if that fails then P&T, then Expansion valve etc, bla bla). One thing I can't get out of my head with all those saying explosions will occur if <u>ALL</u> safety systems fail; how about the strength of the HW pipes leading from the top of the system, or those of the feed?! Would they not burst before the cylinder does?!, surely a 22mm copper pipe or indeed any soldered joints/compression fittings by taps etc would give in long before an unvented cylinder. Comments?