In an earlier contribution to this discussion, andyv
wrote:
I'm trying to plumb up an old cast iron radiator. I've got 2 new 1
1/2" threaded inserts which screw into the body of the rad. Into these
go the valves.

I've used PTFE tape on the threads but don't seem to be getting a
sealed joint on one end. Is there a technique for this? Alternatively
there's a cement called plumber's mait, which I think might be the
sealant originally used on cast iron rads.

Is this any good?

I assume that the leak is on the 1 1/2" thread where the reducer screws
into the rad? This is most likely due to the threads in the rad being
grotty - probably with hardened residues of old Boss White, which are
tearing the PTFE tape.

You really need to clean up the treads with a 1 1/2"BSP tap. If you don't
have one (I'd be surprised if you *did*!), you can make an acceptable
substitute using an old male fitting and cutting some slots at right angles
to the threads with a Dremel or equivalent.

Failing that, you could use gas-grade PTFE tape which is a lot tougher than
the normal stuff. Or you could even resort to Boss White and hemp - which is
probably what was used on the radiator in it's former life.
--
Cheers,
Roger
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