So I maintain there is literally no reason why it shouldn’t go up as well as down to the two motorised valves
The filling loop is on the flow. On that boiler the diverter valve opens when the diverter valve gets up to a certain temperature causing it to open.
I will remain with what I said before get them back as if its firing when both valves are shut it will be a simple wiring fault. Also ask them to put a bypass on it as I said in my last post.