Hi all
I have a plan ... a yen really ... to improve our CH heating system. It
currently has a 4-port back boiler running a gravity feed HW, pumped CH
system. I installed a Sunvic select (207, I think) programmer a while ago,
and replaced the pump with a Grundfoss when the original died.

We do suffer from lack of HW after someone has had a bath etc. I don't want
to change the back boiler, even though I realise it's old-skool.

I have in mind to either:

a) add a Cylinder thermostat and 2-port valve, and convert to C-plan. The
valve will have to be on the return from the boiler, there's no room in the
flow pipe.
b) add a mid-position valve and convert to Y plan (no zoning envisaged).

I've read lots about doing this sort of work on the archives of this fine
newsgroup, and on the wiki. I've also identified all the pipes in the
current arrangement and understand the need for siting the valve with
respect to the flow & return to the F&E tank etc. I do still have a few
questions which might help me decide the route to take. Answers gratefully
received.

1) with my devil's advocate hat on, would there be any real benefit of a C-
plan over our current arrangement?

2) Y-plan seems to be talked of slightly disparagingly in comparison to S-
plan, due to reliabilty problems, difficulty with problem diagnosis, and
lack of zone expansion capability. Given that I don't intend to have any
zoning, are the other problems real (eg. these days)?

3) If I were to change to Y-plan, I understand that I'd need to cap off part
of the boiler. As I mentioned, the back boiler has 4 ports - 2x22mm
(currently CH), and 2x28mm (currently to the heat exchanger for HW). Is this
just a matter of capping off the two 28mm pipes (and moving the feed and
vent pipes) ?

3a) I assume that the reason that the pipes from the boiler are different
diameters for the two circuits is that the larger 28mm dia. gives less
resistance and better allows the HW to be unpumped - is that right?

4) what, exactly, should I be looking for spec-wise in a gate valve, apart
from the pipe diameter? I have a part number for a 2-port Honeywell valve
but I'm curious about what the spec actually calls for. There are a lot of
valves for sale on eBay ...

Thanks a lot in advance

regards
Jon N