Understanding Honeywell wiring centre connections

[D_Hailsham]

If link L1 is present, the cylinder stat C terminal is fed from room stat terminal 1, which gets its supply from programmer CH On. There is then no way you can have separate CH and HW times; it's all controlled by CH timings.

An S plan (two motorized valves) does not require a connection to cylinder stat terminal 2 (satisfied), so I don't know why it is present. Thought: was the system originally a Y-plan?

 

[Alexnh]

I'm not sure, the house is only 2005 and I would guess that the system is all original to that date from the age of the boiler and tank and the lack of any visible modifications to the system and so it has always been a S-plan system.
It is possible that the wiring centre was either re-used from another job or something like that, although a bit odd to reuse such a cheap part? There are some other links that have been soldered together too.

As I've mentioned a couple of times, the programmer's HW on and CH on wires are not connected to the appropriate terminals on the wiring centre but instead link directly to the correct wires using a separate lego type terminal block. Why this has been done is puzzling - it seems to me that the wires are probably long enough to connect to the wiring centre terminals but maybe they're not - it's the only reason I can think of. Anyway that explains why it all works correctly as two separate systems despite L1 being present - nothing is connected to the terminals it links.

So, most of the mystery is resolved, everything is working correctly. Thanks for all the help.