Nest (s) wiring sanity check - multi zone replacement

[Grangey]

Are you sure they’re all neutrals? Seems odd, as when switched off they would become live

I’m not no, I’m hoping the routing per the pic makes more sense of that.

In short - the existing room thermostats have a red and black cable, the black to go to the zone valves, the red seem to go up to the programmer - but changing colour to black as they do.

The other red cables that go from the wiring centre to the programmer, are all connected to the valves “boiler connection” point, with the only trace of the boiler being linked to those blocks being the fact a switch connects to both the neutral bank the boiler and pump does, with the red cable from the switch going to the central connector of those linked connections.

 

[CBW]

I’m not no, I’m hoping the routing per the pic makes more sense if that.

The existing thermostats have a red and black cable, the black to go to the zone valves, the red seem to go up to the programmer - but changing colour to black as they do

Unfortunately, colours mean diddly squat in a heating system - welcome to our world. I wonder if at this point it’s worth getting someone in?

 

[Grangey]

Unfortunately, colours mean diddly squat in a heating system - welcome to our world. I wonder if at this point it’s worth getting someone in?

Well what helps is the pump is in new colours, which along with the valve wire colours which are original, helps very easily highlight the lives and neutrals in the system.

Ive ordered a new wiring centre just to make the entire setup tidy and sleeve the earths, im just missing the link of why there are or would be 6 cables going to serve a ch/ heat programmer, and wondering what the impact might be of omitting some, or the point of this switch and flipping it doesn’t seem to do anything obvious.

If you fancy seeing the unadulterated full colour version of the system- take a look at this

 

[CBW]

No, omitting shouldn’t be a problem, as I’ve never seen one wired the same as yours. However if needed, maybe terminate the blacks at the programmer into terminal strip blocks (individually of course), then if needed, they are available. I can’t follow the full colour system.