In an earlier contribution to this discussion,
Alan Dempster wrote:


So my questions are as follows:

1. The Drayton Tempus 7 seems like a good choice of programmer. But
there's also a similar model, a Lifestyle LP722, which seems similar
BUT it does have a fancy-looking backlit display, which might look
funky in the dark! Are there any differences between these two 7-day
programmers? Recommendations?

Sorry, I've only used Honeywell.

2. I'd like to replace the crusty old Honeywell room 'stat in the
lounge with a new Programmable Thermostat. But is there any point now
that I've installed the Tempus 7 programmer?

It depends on whether the Tempus 7 provides independent *timing* control
over HW and CH - and whether you want this. Many programmers only
essentially have one clock. If you have a programmable room stat, you can
set the Tempus 7 to provide "continuous" CH - and can actually control when
the CH comes on and off with your room stat. This can be at different times
from when the HW is on, and you can have different temperatures at different
times of the day. A programmable room stat also acts as a frost stat in its
"off" position.

3. Should I install a pipe-stat as well as the Honeywell frost stat in
the garage, to protect the boiler? Or would this be unneccesary with a
properly installed Room stat in the living room (probably still
required for boiler protection, I guess).

With the boiler being in the garage, this could possibly freeze up before
the frost stat in the house turns the system on. Maybe *just* a pipe stat -
wired to bring the boiler on when the pipe falls below (say) 5 degC - is all
you need to protect the boiler itself. Your programmable room stat will
protect the rest of the house.


4. How the hell does my HW system manage to regulate its temperature
without any zone valves? The Honeywell Cylinder stat certainly seems
to be doing something....

In a half-hearted way? Someone appears to have attempted to provide a boiler
interlock, but has only done half a job! In HW-only mode, the boiler will
turn off when the HW gets up to temperature. However, in CH mode, the HW
will get hotter than the cyl stat setting whenever the boiler is on.

5. Can I bang a 2-port motorised valve into this system to upgrade it
to a C-plan? I understand that there are venting safety issues with
doing this.. FWIW, the Water Pump is sited directly beneath the boiler
in the garage.

Presumably you have a vented system, with vent and fill pipes connected into
the HW circuit near to the cylinder? You should be ok if you can insert a
2-port zone valve in the the HW flow pipe very close to the cylinder,
*after* the vent pipe connection - thus continuing to provide an
unrestricted path from the boiler to the vent.

The whole thing really does seem like an odd bodge, although I'm
guessing that I could upgrade it to a properly split CH/HW system,
with a bit of extra effort.

You might be able to convert it to an S-Plan system if you can pump both
circuits and insert another zone valve in the CH circuit. Are there
currently 4 boiler connections - with separate circuits for HW (gravity) and
CH (pumped)? If so, you'll either need another pump (and the control logic
then gets a bit complex!) or you'll need to reduce the boiler connections to
3 - by tee-ing the CH flow pipe into the HW pipe a little way from the
boiler rather than leaving it directly connected. You can then put your
(single) pump in this common bit of pipe before the tee. You can keep the
separate return connections.

With 2 zones valves cutting off *all* flow, you *might* need a by-pass
circuit - but that is unlikely with a boiler which can survive with a
gravity system.

HTH.
--
Cheers,
Set Square
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