In an earlier contribution to this discussion,
Mike Barnard wrote:

Hi.

I'm making a new thread because the other one was getting pushed down
the list and lost in the background, and it has raised some new
questions for me.

I have now decided to zone; 2 zones, 1 upstairs and one down. Many
thanks to the posters who have given advice. The house is too small
and tight to put more pipework in than this. Now my remaining
questions are...

1. Can I use a common return? (There was an answer in the previous
thread but it made no sense to me.) If zone 1 is operating and zone 2
isn't, can there be a problem with using common returns?

It's good practice to combine the returns from all the rads in each zone
before combining the two composite returns. Otherwise, there's a risk of
reverse circulation through the zone which is supposed to be off.

2. Can you reccomend a RELIABLE valve to use for just two zones?

Is there also a HW zone (although ISTR that it's a combi boiler, in which
case there won't be)? In any case, go for an S-Plan solution, with a
separate 2-port valve for each zone rather than trying to do it with a
single 3-port valve. Any of the well-known makes (Honeywell, Danfoss,
Drayton, etc.) should be ok. Make sure you get ones with secondary contacts
which close when the valve opens - which you will need for switching the
boiler on whenever either or boths zones call for heat.

3. What about 'primary' rooms and rads without TRV's? As I understand
it, the rad in the primary room (the room with the controls in, yes?
Thats the open plan lounge in my house) should have no TRV. Do I need
a primary room in each zone? What if the controls are in the upstairs
hall which has no rad?

You need a room thermostat (preferably programmable if you want to heat the
2 zones at different times) in each zone. Each thermostat controls its
respective zone valve which, in turn, controls the boiler and pump. The
radiator which heats the space whose temperature is sensed by each
thermostat should *not* have a TRV - but should be fitted with two
lockshield valves so that it can never be turned off. If a zone's thermostat
is not very near to a radiator, it must at least be somewhere where the
temperature is *influenced* by that zone - otherwise the control system
won't work.

4. Websites? General CH design as well as zoneing.

You could do a lot worse than starting with the heating section of the DIY
FAQ at http://www.diyfaq.org.uk/plumbing/he...ngsystems.html


--
Cheers,
Roger
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