Boiler won't fire up for HW only

[Elbow]

Got a client query about a Gloworm Fuelsaver 100F. Won't fire-up when the controller's on HW only, but comes on OK for HW&CH. I'm assuming it'll be a problem with the motorised valve, but is there anyhting else I should be looking out for?

 

[Gunner-rob62]

I'm assuming it'll be a problem with the motorised valve, but is there anyhting else I should be looking out for?

Hi Elbow

Never assume anything.
What type of valve is it?

 

[hammers4spanner]

Timeclock

 

[hammers4spanner]

Multimeter time check signal wires