Draining system on Boilermate 2

Hi All

Right, a couple of questions;

1) I need to replace the emmersion heater which is located at the bottom as its starting to leak, do i just drain the boilermate (isolating the the cold infeed) from the bottom outlet on its own, or do i have to drain the whole c/h system as well?

2) Can i use a common/pattern part heater element as i have never used the element, (only want to stop the leaking) or is it best to buy from gledhill?

3) Upon refill, is it safe to use inhibitor ( fernox etc) put straight into f/e tank, i ask this question as i can find no info on weather the tap hot water is taken directly from the stored water or is coiled inside and simply heated by the water in the tank. Also on the same subject i take it the c/h system must use the water from the tank as the f/e tank replenish's the system when needed.

Turn off supply to F & E tank.
Drain unit using doc at the bottom.
When the water stops.
Fit new heater.
Fill up unit.
Add 1 litre to every 100 litres.
Mike
MGC/H2O
Norfolk

Oh and fit any heater you want.
As you are not using it.
Mike