On Wed, 30 Nov 2005 20:07:04 -0000, "Set Square"
wrote:

The term 'boiler interlock' refers to a method of shutting the system down
completely when both HW and CH demands are satisfied - rather than allowing
the boiler to cycle on its own thermostat when it's not not needed - thereby
wasting energy. In order to achieve this you need thermostats on *both*
circuits plus the logic to shut the boiler down. The easiest way to achieve
this on a gravity system is to install a motorised valve in the gravity
circuit plus a cylinder thermostat on the hot water cylinder, and connect it
all up as per C-Plan shown in
http://content.honeywell.com/uk/homes/systems.htm

The alternative - which is even better - is to convert to a fully pumped
system - either S-Plan or Y-Plan (also shown in the Honeywell link, above) -
but that probably requires extensive plumbing mods whereas the plumbing for
C-Plan is minimal.

Make sure you don't have a Primatic cylinder if you go for this
option!

Mark.