I live in a house that had Nu-Heat underfloor heating when we moved in (in 2001). It's leaked. Lots. I had replaced the upstairs heating with conventional radiators when I first wrote this page years ago, and I've since done downstairs as well (almost - the study/library I did when it turned into a home office because of Covid-19, but the family room/kitchen only has one small radiator, so the wood-burning stove is not just for decoration. (We did fit it because the heating wasn't working when we first moved in, but that turned out to be just a pump that needed replacing.)
(The alternatives were to put new underfloor heating on top of the existing floor and a new floor on top of that, or to take all the downstairs ceilings down and fit underfloor heating from below. I favoured the latter approach, but the rest of the household disagreed. Taking up all the tongued and grooved chipboard which extends under the internal walls was not an option; doing the small sections necessary to get at some of the leaks before total replacement was bad enough. Downstairs would mean taking up solid wood floors, and doing that neatly enough to reuse the wood almost certainly isn't a DIY job (nor would fitting a replacement with new wood).)
You can read more detail over at Dreamwidth or at least those bits of the problems that happened after livejournal introduced tagging or that I had gone back and tagged. (And some of the problems were from before I started using livejournal at all, like the coils in the cylinders going so those needed replacing to stop them continuously pouring hot water down the overflow pipe (replaced with pressurised ones with an expansion vessel, since they no longer did the old style with atmospheric pressure feed tank on top).) http://www.diyfaq.org.uk/plumbing/plumbingpage1.html#thermal explains the general principle of the thermal store tank setup. (One day I want to integrate solar thermal panels with it, but that's another story.)
You can see some other people's problems at http://www.ebuild.co.uk/community/topic/4371-problems-with-nu-heat-underfloor-heating/
At least in theory the new (FastFlo) pipe material doesn't have the same problem as the rubber hoses they were using ten years ago, and the current warranty terms are better. And Nu-Heat have been generally helpful, and sent repair materials promptly, for free. But if you are thinking of buying a house with an existing system, beware. (Apparently the problem is at least partly caused by copper, so replacing the manifolds and cylinders with stainless steel ones might stop things getting worse if yours isn't leaking yet. I hate to think how much that would cost though.)