book yourself on this course
http://www.worcester-bosch.co.uk/installer/training/industry-focused-courses/chemical-water-treatment-course
remember you will need to know the internal quality of the radiator to make any guarantees, it could be rotten inside and could foul the system days...
I would say there is 2 wires in terminal 1 as well. Looks like original installer has used very small dia cable and doubled up the conductors. :?
But it's working now.
Online calculators are very unreliable. The best way is yell.com a professional will carry out all sizing correctly and installation. Don't waste time and money trying to save time and money.
Made a fair few mistakes in your description, it's clear to me what your thinking but your in the complete wrong area.
I recommend yell. Com. It's full of highly trained professionals with a wealth of knowledge and eager to assist you
Dan that install is nice But the grey waste is a poor colour choice. And do those lever valves including the all important gas one fall to the ON position?