Bypasses, Room thermostat or flow switches all of interest as I am
sorting out the spec for my replacement system.

The TRVs + flowswitch plus Grundfoss Alpha does seem the logical
approach - I hate the single room thermostat approach and find that in
the type of houses I have had they are useless at providing sensible
control of when the boiler is required to be providing heat.

but re Grundfoss Alpha pump and bypass

Can the pump in condensing combi boilers such as the Worcester and
Valliant range be replaced with a Grundfoss Alpha or are you stuck
with the "manufacturers" specified type ?

Robert