On Tue, 31 May 2011 23:32:59 +0100, The Night Tripper wrote:

1) with my devil's advocate hat on, would there be any real benefit of a
C-plan over our current arrangement?

In your current arrangement the HW is heated whenever the CH is on.
The water circulating in the CH circuit should be around 70 to 80C,
this rather hot (scalding hot) for HW which would normally be around
60C.

Whenever the HW is on the boiler will cycle to keep the boiler and
gravity loop hot. Both of these "features" waste energy.

A tank stat could be fitted that would solve the last but not the
first.

--
Cheers
Dave.