ok thank you, so if the pump isnt wired back to the boiler will the pump...(A) still run if wired soley into the 10 way box? and (B) if it does still run will it run constnatly causing the water to circualte around the by-pass/circuit (depending how the 3 port valve is positioned) thus causing the boiler to re-light everyso often to heat the water to temp ? thanks in advance.
(A) Depends on where it's connected to in the 10-way!
(B) Same answer as (A)
The pump's Live should be connected to the Vaillant's "L for pump", the Pumps Neutral (and Earth) don't have to be connected directly to the boiler, as long as it's a common Neutral in the wiring.
I've just re-wired my Vaillant ecoTEC 418 and confirmed the above via Vaillant tech before doing so.