Automatic bypass Too many?

[Failte]

Have a Vaillant Ecotec630 Plus 30kw lpg boiler year old fitted to UFH downstairs and 13 rads inc 5 towel rads all with TRVs The question is the boiler has an internal automatic by pass and one is fitted externally, but with UFH by default there is a bypass at the pump/manifold to the UFH. could all the by passes contribute to poor Rad performance at the Rad furtherest from boiler. Should they be adjusted turned up or shut off completely.

 

[SJB060685]

Any sort of bypass can cause flow problems if not set correctly or not needed yes.
With the UFH off and all other rads/towel rails off does the furthest rad then get hot?