Hi, I had a problem with my radiator valve in the living room and a friend fixed it for me. I was wondering if he needed to use a radiator tail or is it ok to screw the TRV straight into the radiator? Also after he replaced the valve there is gurgling in the radiator upstairs in the bathroom. I have bled the radiator lots of times but it keeps gurgling, is this something to do with the radiator tail. Thank you