On Thu, 29 Oct 2009, John Rumm wrote:

Kostas Kavoussanakis wrote:
On Wed, 28 Oct 2009, John Rumm wrote:

Does modulation happen anyway as a result of demand variation, or
does one need suitable room or external sensors?

No, modulation will happen anyway. Without a weather compensator,
the boiler will maintain a set flow temperature, and also possibly
attempt to maximise condensing efficiency by keeping the return
temperature lower if it can. So as the return temp creeps up it
modulates the power down.

Thanks. So (having read the other thread, where it was claimed that,
for the W-B at least, there is no real gain for domestic
applications) is there no particular gain or timely return of
investment from using the modulating thermostats and weather sensors?
Judging (from an ignorant POV) by the wiring diagrams of the VR61,
it could be quite a task to set this all up.

Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 +
Vr 61 2 Heating Zone Kit, or can I just add another zone using any
stat and a valve?

The VR430 is usually about £100, and the VR61 about £70. There are
quite number of ways the above beasties can be configured, for
multiple zones - some offering temperature mixing for things like
UFH. You could (I expect - not read through in detail) do a bog
standard S+ plan system with ordinary stats and zone valves for a
fixed flow temperature all over.

What does "fixed flow temperature" mean in this instance? I could
perhaps desire to not heat a zone too much in the mornings, but heat
it more in the afternoon; is that out of scope?

So many options, such high costs...

Costs are not so bad if you shop about a bit.

http://www.plumbnation.co.uk/site/va...or-0020028520/
http://www.vhsdirect.co.uk/product/vr_61_mixer_module/

Thanks, I had seen that, but in browsing the literature it seemed to
me that you need more that a 430, a 61 and a 81 for two zones (and was
thus attracted to the kit). I guess I was wrong. Meanwhile, the CM907
is 50-55 quid.

Cheers,

--
Kostas