Hi Andy and thanks for the response.
I traced the cables back to the circuit board from the valves and worked my way back from there.
They are controlled by a bank of Triac's and MOV's triggered from the main microcontroller.
One of the triacs had gone bad, i isolated this just using a basic diode check function on a multimeter which indicated that there was no voltage drop across the component.
Replaced with a new triac (Z0107NA if anyone is interested) and all is well again!
Its not something i would recommend unless you have experience with soldering electronics as these components are heat sensitive and easily damaged whilst fitting.
Ive tested on each cycle now and none of the programming seems to have been affected either.
Thanks for the quick response anyway and have a nice day!