Potterton Suprima no hot water unless central heating on too

[MANDATE]

On room stat diagram, The white goes from the on terminal not the off. In fact there is no off terminal, it's not a two way.
The cylinder stat is correct, but its shown it in a satisfied state.ie 'com' to 'grey'.
If it was not satisfied the switch would be from 'com' to 'orange', which is where you need to bridge across