We agree there should only be 2, this is the problem.
We do not know where the back feed is coming from.
We have a Vaillant 428 using a Siemens programmer.
Used the Y plan wiring guide using the boiler as master supply and pump overrun independant.
Why am I getting 3 lives on my cylinder stat connections?
This should only be two, I have gone through the wiring guides and not found either faulty wiring nor products.
Honeywell technical closed for Xmas.