Combi boiler mystery issue

[Deleted member 120897]

Sorry I didn’t explain that clearly: back when it was working well, I would flick a little knob on the timer to switch the heating on/off/via the timer dial. That sends an electrical signal to the PCB which then must send some water through the diverter valve (since the diverter valve has no electrical inputs itself, it’s behaviour must be governed by what water is flowing, and from where). So what is it that the PCB does (under normal working conditions) to draw or push water through the diverter when CH is turned on?

Hope that makes sense!
Thanks, Greg

Try reading this - the pump and flow switch