In an earlier contribution to this discussion,
The Wallport wrote:

OK - I have installed a Drayton Tempus 7 and it seems to be working.
Wasn't backplate compatible so had to rewire but this was fairly
simple. Of course there was no wire to connect to the heating off
connection - I hope this is OK but can't see how it's any different to
before.

Don't understand the full meaning of the term "Two channels" but if
this means ability to control hot water on/off and heating on/off then
yes it could do this but there was only one set of times available for
on/off.

Don't fully understand the Y plan but I did trace the wires to a
junction box and the hot water off wire does connect to a valve which
I presume directs the boiler output away from the hot water circuit
when it's off. I don't understand what happens when the heating is
switched off but the water is switched on.

Anyway, all seems well for the moment - unless anyone is going to warn
me of something I've not realised!

G.

You don't need a CH connection but you *do* need a HW off connection if it's
a Y-plan.

Yes, 2 channel refers refers to independent switching of HW and CH - albeit
at the same times, because there is only one clock. But it does usually
allow you to have (say) 3 on's and off's for the CH but "all day" (first on
'til last off) for HW - or vice versa - or to have one or other or both on
constantly, ignoring the clock. Hence if you have a programmable thermostat
for the heating, you can have CH on at completely independent times from
HW - using the original programmer clock for HW amd the clock in the stat
for CH.

With HW on and CH off, the 3-port valves sits at its rest (unpowered)
position - where it directs the boiler output only to the heating coil in
the HW cylinder. In this position, the boiler and pump are powered from the
programmer and cylstat - rather than from the microswitches in the valve
actuator.
--
Cheers,
Set Square
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