"Dave Osborne" wrote in message
...
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.

That would be good. Zoning of CH is becoming more common. Possible problems
would be the way the CH zones are controlled. Some installers use three
channel programmers (or extra programmers) and others just use extra room
stats that are controlled by just one programmer.

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

Probably the most common set up now on a new regular boiler. Yes that would
be a good one to go for.

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

Not sure about this one. I have added pump over runs but only because a lack
of available cables down to the old boiler and the customer did not want
kitchen tiles smashing off the wall etc.


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.

Maybe. But a system boiler usually only needs Permant Live, Neutral, Earth
and a Call Live. The pump is taken care of internally by the boiler PCB

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?

It is a valid way of wiring a boiler. Unless someone comes up with a genius
"all in one" diagram then I suspect that there would be too many variables
to make this a viable option. The system could consist of a mixture of
remote and hard wired thermostats and it is not possible to cover all
aspects.

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?


If you do not mind hand drawn scanned sketches then no problem.

Adam