Hot water priority question

[desktop987456]

With a regular 2 pipe boiler (flow and return) an external valve is required to divert the primary water.

I have a two pipe heat only boiler (viessmann) so a 3 port valve is required to run PDHW, but that would be a Y plan or PDHW?
What is viessmann cylinder demand box used for (see attached instructions) and I am confused about which configuration to run.
As OP, I am in similar position and trying to figure which components to buy and for what configurtion.

 

[Madrab]

I have a two pipe heat only boiler (viessmann) so a 3 port valve is required to run PDHW, but that would be a Y plan or PDHW?
What is viessmann cylinder demand box used for (see attached instructions) and I am confused about which configuration to run.
As OP, I am in similar position and trying to figure which components to buy and for what configurtion.

Can I suggest keeping one question one post - it can get really confusing for everyone if another question crosses over some one else's post