On 12/28/2016 4:46 PM, DerbyBorn wrote:
Is an immersion heater one of those situations where - as it is the washer
and the faces that perform the function of sealing, it is totally un-
necesary to apply any sealant to the threads. (I wouldn't - I would just
ensure the faces were free of debris and damage - and the washer was good.)

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.