robert wrote in message ...
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 ?

Some makers say you can fit them as a direct replacement. Others say no, as
they don't want any deviation from the norm. In most cases you can replace
like for like if it fits in. There is a larger control box on the Alpha.

Using an Alpha with an auto by-pass sometimes may not open the auto by-pass.
See this page of auto by-pass setup:
http://www.grundfos.co.uk/web/homeuk.nsf/vDocumentsDescending/8DBC6A2C79D5E6EF80256F7B00321AD3?OpenDocument

A flow switch with a settable by-pass around it is the best option when
using an Alpha pump. Or if you can get a flow switch which switches off the
burner when flow is below the minimum the boilers makers stipulate.