Mum and dad's heating control system has never worked properly inthe 31
years they've been in the house. Several heating-types have tried and
failed to get it working under timer control without success. Now it's
my turn. I spent an hour this evening figuring it out and discovered
that the main reason it doesn't work is that there is no permanent live
supply to the timer clock! Now this is easily sorted, BUT...

....the 3-port valve is arranged so that when it is *powered* boiler
output is directed to the radiators and when it is *unpowered* it heats
the hot water.

As part of my sorting out I'm going to be fitting a new timer and a
timed room thermostat, but I can't work out a way of doing this which
gives HW priority (surely desirable) unless I can somehow swap around
the action of the 3-way valve. Is this possible without physically
turning the whole thing around which will need a drain-down (unless the
gate valves work)?

Or have I missed something blindingly obvious?

Quick ASCII-art of current setup (ignoring the non-working timer):


LIVE -+-- CYLINDER STAT (NC) ---- 3-WAY VALVE ---- N
| (NO) --+- PUMP ----------- N
| |
+-- ROOM STAT -----------+

Or to put it another way:

If the cylinder stat is off (no HW demand) then the flow is through the
radiators, if the room stat is on and supplying power to the pump.

If the cylinder stat is on (HW needed) then the flow is through the tank
coil, and the pump is powered via the cylinder stat, whether or not the
room stat is on.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
.... "Bother", said Pooh, as he saw the mushroom cloud.