On 14/05/2021 20:56, Theo wrote:
A house I used to live in had an early 1970s cast iron lump [1] for a boiler
and a mechanical time clock. One 'feature' of this system was that you
always heated the hot water when you turned the heating on. I understand
that was common in older systems.

I'm curious as to how this was plumbed. I understand about S and Y plan
systems, but I can't see how that would cause this effect. Was this set up
with the boiler output always going through the coil first? Or with a
single heating on/off valve? Or was it an S plan where the controller just
told the hot water valve to open when the heating was on?

Anyone know?

It was quite common to have a big cast iron lump HX with high water
content (couple of gallons). That would have 4 bosses on it - two
outputs and two returns. One set would be used for the feed and return
on the pumped circuit through the rads, and the other two would be used
for a gravity (i.e. convected circuit) to heat an indirect cylinder.

The convention circuit required that the hot water cylinder would be
placed some distance above the boiler and not too far displaced from it.
It would also typically be piped in 28mm pipe to better allow convection
flow. Hot water from the gravity output would rise up through the pipe,
and through the coil in the cylinder, the heavier cooler water would
fall and return to the boiler. Basically it sets up a thermosyphon.

Some refinements of the system introduced and anti gravity valve to stop
heat being lost out of the cylinder through the boiler when it was off.
Some had a kind of thermostatic valve in the gravity loop to limit the
maximum temperature of the cylinder DHW. Some would add a motorised
valve to make it a fully controlled zone. (aka C plan)

[1] Potterton Kingfisher I think it was, although I gather there have been a
lot more recent Kingfishers since then

Yup, I know someone with one of those and a gravity circulation loop...


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/