I had an unpleasant surprise when I removed a TRV yesterday - water started to come out, as did the valve pin. Replacing, and screwing down, the TRV stopped the leak. There's a thin white plastic ring around the pin but I can't tell whether it's broken off from something inside or whether it needs to be screwed back into the valve body. I can't find a drawing of the valve innards so I'm hoping that someone here has had one apart and can explain.