On 15 Feb,
Roger Mills wrote:

I can think of a way which *might* work - but you'd end up with a highly
*******ised system which future generations (or even the present one!)
might not be able to understand!

When I fitted my current boiler 18 years ago my supplier didn't have any 2
port valves in stock, so I opted for 2 3 port valves instead of 3 2 port
valves. Upstairs CH, downstairs CH and HW. It worked, but certainly was
non-standard. I could figure it out but J. Plumber probably couldn't. I put
circuit on lid of wiring centre.


How about if you split the CH output from the 3-port valve into 2
circuits, with a 2-port zone valve in each - one for the radiators and
one for the UFH. Control these valves a bit like in an S-Plan system,
with the radiator one being controlled by the CH room stat and the UFH
one being controlled by a new? roomstat[1] in the conservatory.
Now the clever bit. . (I think!) Parallel the auxilliary contacts in
the 2-port valves, and connect them into the circuit where the Y-Plan's
roomstat used to be.

The 3 port valves, particularly the one on the heating zones, proved to be
unreliable (the micro switches failed, I had a spare head and changed one
about every 6 months. After about 3 years I replaced the heating zone one
with two 2 port valves wired as above. These worked well until about 3 years
ago, when small leaks developed around the stem of the water part. The hot
water valve had been modified to be a divertor, losing the mid position, when
I replaced the first 3 port valve with 2 port valves. In this mode it was
reliable. Over the last 3 years all valves have been replaced resulting in an
almost standard s+ plan, modified to give hot water priority using back
contacts of HW thermostat and timer. This is reliable.



That should give you independent control of the radiator-based and UFH
parts of the heating system, still with boiler interlock. However, you
still might need a bypass if the boiler needs pump over-run because
there would no longer be a guaranteed flow path.

Boiler had bypass, pump run on not needed, but I added an external bypass at
a lower setting which is adequate and quieter.


[1] I assume that the UFH's thermostatic valve is mechanical rather than
electrical, otherwise you might be able to use that instead of an
additional room stat. If it *isn't* being used - either by my 'solution'
or if you go the full S+ Plan route, it's probably best got rid of.

Don't (yet) have such beast, UFH is contemplated for kitchen and dining room.
I'll probably wait until the current boiler (18YO gloworm fuelsaver complheat
system boiler) is replaced by a condensing one once I can no longer fix it.

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