Nest and Weather Comp Logic Max System 2

[telerob]

Morning, quick question - I am going to add weather comp to my existing setup (Logic Max System 2, S Plan, 250L tank, with Nest) however the installation diagram shows SL2 In to HW off as triggered by the cylinder stat.

However, there is no HW off wire from the cylinder stat at the moment, and nothing attached to terminal 4 on the Nest which is HW closed/satisfied. The question I have is when I add the 3rd wire for DHW off from the CS then to SL2 In, do I need to add a wire to terminal 4 on the Nest as well or will the Nest be happy with T4 left alone?

(The Nest heat link has been installed with terminals 2 and 5 connected to SL1 Out, and although I'm inclined to want to tidy that up and just link T2 and T5 to L on the Nest, I think I'll leave that alone with opentherm looped and untouched until we switch to OT in the future to see which works best for our needs)

 

[RandomGrinch]

The question I have is when I add the 3rd wire for DHW off from the CS then to SL2 In, do I need to add a wire to terminal 4 on the Nest as well or will the Nest be happy with T4 left alone?

I'm afraid I don't know much about this system - but logically (and electrically),
If the hot water has been off for a while and the cylinder is cold, the cylinder stat would be switched to 'CS/on', even if hot water wasn't called for from the Nest.
There would be no live connection to SL2.
With the terminal 4 link to Nest in place, SL2 will receive the live from terminal 4, even when the cylinder is cold.
This may, or may not be vital for weather compensation, but it's probably worth putting the wire in!