"Andy Hall" wrote in message
...
On Wed, 3 Nov 2004 20:56:25 -0000, "IMM" wrote:


"Ed Sirett" wrote in message
news
On Wed, 03 Nov 2004 10:42:10 +0000, IMM wrote:


Some of the control systems that are now being used in some boilers are
a
significant (even you might say a quantum) leap ahead than simple
on/offs.
Some of them are sophisticated enough to work out a good enough
strategy
simply from the on/off signal and the return flow return temperatures.

They do and that is designed for the heating function. DHW usually
throws
them, unless they know it is DHW by a signal from a stat.


Which is not that hard since something will be switching motorised
valve(s) anyway.

I have mine set up to work the opposite way around to conventional
Honeywell plans

The boiler is given outside temperature, cylinder temperature and room
controller data as inputs. There are a choice of functional
programs for different valve or external pump configurations using
three relay driven outputs.
I use one where the boiler has control of opening heating motorised
valve(s) or DHW valve as required - in effect an S plan configuration
but with the boiler acting as controller and no auxilliary contacts
used.

When a hot water cycle is needed as monitored by the cylinder sensor,
then CH valve is closed and HW opened together with full power.
On completion, the CH operation is recommenced by closing the HW valve
and reopening the CH.

You have a state of the art boiler, most cheaper versions: Ideal, Glow Worm
etc, do not have a simple function to bypass the modulating control system
and keep the burner full on. Or a function to tell the control system that
what it heating is not the heating circuit, so any self adaptive memory must
not be used. Ravenheat of all people, even have this.