According to the instructions on a new TRV I have purchased it says that if fitted in a vertical position, it should be on the water input flow end. On checking my 5 rads, only 1 was fitted like this on the other 4 the TRV wasfitted on the output flow end. These have been like this for at least 10 years and appeared to work correctly. Does it really matter which end they are connected too. Thanks for any replies and advice.
I take it you went round all your radiators and held each pipe to find which one was hottest it's about the easiest way of finding out which is the feed pipe to your radiator,it is best if the TRV is on the feed but will work okay if not,if it bothers you wait for the summer and drain system down get some new valves and swap ends