Roger Mills wrote:
my boiler only has two water pipes

The diagrams are *schematics* - showing how they *function* rather than
exact representations of the pipework. With the exception of W-Plan they all
show 3 connections to the boiler. But it doesn't take a lot of imagination
to visualise what they would be like if you combined the HW and CH returns
before taking then back to the boiler. There would then only be 2 boiler
connections, and they would look more like your diagram.

I know they're functional schematics, but, probably because I'm an
electrician, I tend to expect functional schematics to have some
relationship to the equtipment they represent. A central heating
pluming circuit is essentially a parallel lighting circuit - live feed
out, tee off to emitters in parallel, return back to source.

see http://mdfs.net/Docs/Plumbing/Heating.gif
That's useful - I can see what you've got, and it almost certainly pre-dates
any of the standard Honeywell 'plans'. In the 60's and 70's, the 'norm' was
to have a gravity HW circuit and pumped CH circuit. What you have is one

Everywhere I've lived since 1969 has been like that (except the one
place I lived which had no heating at all. Get up, fill coal bucket,
get fire started...)

interlock - as provided by most of the 'plans' - and the thing is that it
would be so easy to update it to take advantage of a much better control
system.

My boiler's been wearing out and I plan to get it replaced, and moved
to a more useful location. The plumber can put in whatever system
is appropriate - as long as it still give me a tank full of hot
water

--
JGH