On 07/05/2010 16:28, Roger Mills wrote:


The essential characteristic of S-Plan is that each actuator motor is fed
from the programmer via its respective thermostat, and the auxialliary
contacts are wired in parallel - with one side having a permanent live feed
and the other side connected to the boiler's switched live demand. Both
diagrams show this - the only difference being where the permanent live feed
comes from. In yours, it comes from the heating control switch and in
Vokera's it comes form M7/2 on the boiler which - if you look at Fig 31 in
Section 8.1 of the manual, is almost certainly permanently live.

Lets take the auxiliary contacts: They need to be fed by a permanent
live feed, and the other side goes to M7/3, which is the demand for heat.

gotcha! :c)


There is no link connecting the Live wire, in the timer, to any of the
pins numbered 1 to 6. Presumably the Live potential is coming from the
boiler -out of the black wire.


That bit's a complete mystery to me! That other black wire is almost
certainly a live feed to the switching contacts in the programmer - but I
haven't a clue why the main live feed to the programmer isn't used instead.
Where on the boiler does that black wire connect?

Is the schematic I've drawn out correct?

Probably, but the feed to the progammer remains a mystery.

M7/2 MUST be a permanent live feed. As you basically surmise. Really,
what is happening is this: Your regular heating engineer would feed the
auxiliary contacts with a permant live feed from M7/2. The permanent
live feed for the timer switch contacts would come from the heating
controls switch.

But in this case the installers reversed the permanent live feeds.
Taking the timer live feed from M7/2, and the auxiliary contacts live
feed from the heating controls switch.

As you probably realised, but I've just. :c)

What MUST be the case, is that the installer HAD TO KNOW which black
wire went to where. Otherwise chances of working were 50/50. :c)

I think I got it now, and feel confident the schematic is as the system
was wired before I removed all the wiring connections.

I'm now going to wire it up again.

I've learned something. :c)

Thanks a lot all. Rich