Hands up, I've caused a problem for myself. When changing a rad I snapped off the tip of the lockshield valve when it seized shut. I now need to replace the radiator valve preferably without draining the sealed combi system. Can it be done? I've thought of pipe freezing, but can't find a kit and have no idea how much it costs. I've thought of removing the valve top and replacing it very quickly? I've also thought of fitting a push fit pipe isolator inline with the valve to give me time to change the valve, but I have no idea if any of these (or other) ideas are viable. Ideas please, hopefully one without making to much of a mess.