Hello,

I have fitted thermostatic valves to all my radiators. Some, being old, needed
a 3/4 OD x 1/2 ID brass bush between the radiator collar and the new valve.

The bush does not tighten on the valve until the flats meet the body. Also the
bush is not flanged and does not match the profile of the 'sticky out bit' on
the radiator therefore there is only a sharp edge seal. I used what I thought
was adequate PTFE tape to seal all threads but the bush weeps water through the
inside diameter of the bush.

Q. How many turns of PTFE tape should I use?

Q. Is there a better method to seal threads like this like some stuff that
swells when it gets wet?

Many thanks

Andy
(Thanks to all posters re boilers by the way)