Roger Mills wrote:



Excellent!

I wonder whether it's worth adding one additional refinement to reflect the
way in which many systems are *actually* configured? I'm referring here to
pump over-run arrangements. Your diagrams faithfully reproduce the original
Honeywell 'plan' details - with the boiler and pump wired in parallel in all
cases. However, many (most?) modern systems ain't wired like that, but are
wired as follows:

The boiler has several additional terminals - permanent live, plus N, E, L
for pump connection, and the terminal shown as L on the diagrams becomes a
"switched live" (demand) to distinguish it from permanent live. The pump is
then, of course, connected to the boiler's pump terminals rather than as in
the diagrams.

[This enables the boiler to control the pump, and to keep it running after
the demand has been removed in order to carry away the residual heat].

I would suggest that if you take up this idea, the modified diagrams should
be in addition to the original ones rather than replacing them so that, for
example, we might have Basic Y-Plan *and* Y-Plan with pump over-run, etc.
The schematic for S-Plan (and S+) with pump over-run would also need to
include a by-pass circuit.

Well, I'd be willing to bet that there are many millions of systems out
there wired to a classic Sundial plan. Mine is, for one... :-)

However, I'm quite happy to do additional drawings for more modern
installation arrangements.


From my limited reading, the following ideas come to mind:-

1. Wiring diagram for S-plus with one and two extra heating zones.

2. Conventional (i.e. not system) boiler with pump-overrun timer (as you
have suggested above).

3. Classic Y-plan, S-plan with retro-fitted separate pump overrun timer.
(e.g. Broyce Controls M1EDF RS 296-7393).

4. System boiler? I'm kind of assuming that these come with wiring
diagrams and have "wiring centres" built in, so the programmer (if
external) and the thermostats connect directly to the boiler.

5. Versions of Y, S and S-plus where there is no central timer, just
programmable thermostats. Is this even a valid way of wiring a system?


I would need someone or three to commit to assisting with providing
suitable source material (including sketches) and/or reviewing and
commenting on draft drawings as I am no expert on central heating controls.

Any takers?

DaveyOz