I may have solved it so thanks for your help. It looks like the CH pump is at fault. This comes on at the same time as the motorised valves/actuators. Having isolated everything it seems as soon as the pump comes on then the fuse goes.
Damn!
I have replaced the ST699 with the Drayton Tempus 7 mapping the wiring as follows:
N to N
L - L
8 -HW on (3)
5 - CH on (4)
I have ignored the linked wires to the Com terminals.
Problem I have is as soon as the Actuators kick in I blow the fuse?
Any ideas what I have done...
