There were some questions about this many years ago but I will ask again. I am replacing all my rads over a number of months and have avoided draining down as I have kept the old TRV's and lockshield valves fitted as isolation. However, in one Instance I need to lengthen a pipe by about 100mm. Pipe is 8mm and as I am lengthening the pipe, I will replace the lockshield at the same time. The question is whether it is worth trying a freeze isolation before resorting to a full drain down. Job should be very quick, I will have the new valve ready with the right length of new pipe fitted. It will then just be a case of cutting the existing pipe and joining with a compression joint, hopefully a five minute job. Any advice welcome.