Hi SS, any chance of a drawing? Sounds like you need to separate the room stat and CH pump from the boiler L, but I'm lost on the existing wiring set up.
Haven't got a drawing as such buddy, but can explain what I have / seems like !
Looks like it's trying to be a C+ plan,
but the install was a mess, I have stripped it all out and reconnected as it was but with new valve etc..
From the boiler only the heating has a circ pump on it straight away then onto a 2 port valve HPA2, this in the garage next to new wiring centre, the nest heat link and the mains etc..
The dhw side is gravity only to upstairs airing cupboard in the house with an old range hercal type blue foam cylinder.
It had a twin and earth feed, neutral and earth only up there which fed the cylinder stat and then closed to fire the hw 2 port valve on cylinder pipework. There was effectively no switch line back to fire boiler, so I have provided a switched line back via RF link.
Old way was that when cylinder stat called for heat and opened the hw valve the hot water pretty much trickled through until the boiler lost heat and internal stat closed to pull boiler in again.
Room stat was old 240V fed Satchwell/Sunvic so switchline there opened heating valve, fed boiler L,N,E. and link inside a pattress blanked off fed the circ pump too.
Now the nest I have installed does the same job calling in the valve and have wired the microswitch on a new HPA2 valve to switch the boiler and link switches the feed also to the pump for heating.
Problem arises when the RF linked switchline returns to wiring centre and calls boiler for hot water only it then feeds 240V via the link between boiler and pump and pump starts up. The heating side is sat at 0V as satisfied and so pump would be pumping flow against closed heating valve. So I have had to revert back to the old way again as can't work out how I'm going to get boiler to fire separately from the switch line from bringing pump on. Hope this makes sense, and thanks for taking the time out.
