Replacing an immersion heater

I did that, and it is exactly as you say. Afterwards, I read that fibre washers of that era contain asbestos. Oh well, fingers crossed. You seem to have survived ok. :)

True but it is damp and the dust doesn't waft about.

I think that is a good point.

Possibly I was misleading and the jointing compound was applied to the washer.

The first time I refitted the immersion I didn't use jointing compound and it leaked. So I put jointing compound all around it the next time. I bought a better spanner too, so I can't be quite sure what fixed it.

Only taper threads make a seal. Parallel threads are not intended to and need a washer or joint.

But if it had been fitted by someone who used a thread sealant than it won't help much.

True, you don't need it for sealing. But if you use PTFE tape, this reduces the friction and then you get more axial force (so better sealing) for a given torque. And if you more or less completely fill the thread clearance with PTFE, you get less limescale deposited there, and that makes it easier to remove. PTFE is so soft that you can't really overfill the clearance, any surplus just extrudes. The same think happens if you accidentally put a wrap of PTFE over an olive, although it is good practice not to.

IME yes, its much stronger when kept "taught" by the mass of water in it.

Oh dear, I don't think this is going to increase my popularity, 'taut'. (It does mean you don't have to quote it really though).

:-) :-)

That's virgin on tautology.

Apologies - fumbled it as I typed, and then took the first spell check option without looking carefully enough!

That's taut you!

Although it has left him barking mad! ;-)