On Sun, 21 May 2006 10:08:05 +0100, Doctor Drivel wrote
(in article ews.net):


"Andy Hall" aka Matt wrote in message
...
On Sat, 20 May 2006 19:02:49 +0100, Doctor Drivel wrote
(in article ews.net):


"Andy Hall" aka Matt wrote in message
...
.

- As soon as there is DHW demand, the boiler
cuts power to the second output, closing the CH
zone valve(s) and powers the first output, opening the
cylinder zone valve. It then fires up to full output
and flow temperature rising to 85 degrees output.

Matt, how does your boiler model know
that DHW is calling if fitted with
either a stat or temp sensor?

There is a setting on the controller in
the boiler to select whether the DHW
demand sensing is by a contact closure
(i.e. thermostat) or a temperature
sensor.

When a stat detects DHW is calling the boiler just then runs up to what the
maximum temperature the boiler is set at?

Exactly.


Demand sensing - this will be a
DHW setpoint (cylinder temp) set at the boiler. Below and the boioer runs up
the the max boioer temp set?

Yes again.



There is a similar one for CH control
where the sensing is between thermostat
contact, a PWM signal from a Siemens or
other controller or 0-10 or 0-3v analogue control.

External control which incorporates the burner modualtion rather than
on-off.



Yep. (You're getting good at this :-) )

The Siemens (was Landis & Gyr) RE2132 controller which is specifically
intended for this boiler, AFAIK, (possibly special firmware), has a setting
to adjust the relative balance between the external weather sensor and
internal sensing. Thus one can have different response behaviour according
to nature of house. It takes care of optimised start as well.

The other input methods are used in commercial applications when multiple
boilers are cascaded and a cascading controller is used to handle up to 9 of
the boilers.