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.