Set Square wrote:

Does your loft have lots of headroom? Assuming that you're not going
for a
mains pressure hot water system, you'll need to get your cold header
tank
*above* the level of the hot cylinder. This will need supporting
*very*
well - water is heavy stuff!

The intention is to try and get everything mounted above a supporting
wall. The loft has enough head room for the cylinder plus a bit more. I
was planning to get the water line for the header tank a few inches
above the cylinder ... should I really be aiming to get the whole tank
above the cylinder?

If you're going fully pumped with a single pump, you'll need both HW
and CH
to share a common flow pipe until after the pump - where the circuits
then
split using zone valves (S-Plan) or a 3-port mid-position valve
(Y-Plan).
[See http://content.honeywell.com/uk/homes/systems.htm]

At the moment, the pump is directly above the boiler. My original plan
was to put a 3 port valve directly after the pump and run a new 22mm
pipe run straight upto the cylinder in the loft. This seems the
simplest approach as it involves the least modification to existing
pipe runs.

If you currently
have separate circuits (4 pipes into the boiler) this will need
changing.

Yes, it has 4 pipes. Is it a simple case of capping off the existing
pipe for the gravity cylinder? Or does it need to be a circuit with
water in to stop the boiler over heating?

If your boiler can stand it, you might consider converting to a
non-vented
(sealed) primary circuit - using a pressure vessel and filling loop,
and
getting rid of your small F&E tank.

Is the advantage here that you're losing the tank or is there an
additional benefit?

Thanks,

Don