Pulsacoil A Class - changing the immersion element and Filling up the Pulsacoil

Hi,
It is probably a silly question but which should I use when installing a new immersion heating element - PTFA liquid or PTFA Tape or something else.

The other question is - What is the proper way to fill up the Pulsacoil tank once it has been drained down. Would I need to keep topping up the Header tank untill the boiler is full or there is other way to do it properly. How do I know that the tank is full and no more water is required?

I would appreciate if someone could answer the questions above and maybe shares some tips on the above job as well as potential issues that may occur during this proces.

Many thanks in advance for your help.
Rafal

Undo the heaters (loosen when unit full.
Then drain
Remove heaters.
Put jet blue or similar on heater boss
Then gasket
Then more Jet blue
Insert tighten not too much.
Wipe off surplus.
Fill and bleed pump.
Drain off could be blocked or slow.
About it
Mike