Can I electrically "reverse" a 3-port valve?

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.
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A three port valve has three positions arranged like:
HW port closed, CH port open. HW port open, CH port closed. Both HW and CH open.
So it is more likely that the valve is either faulty, or has not been fitted on the pipework correctly, to show the symptoms you're describing.
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Not all three port valves are mid-position valves. Mid-position valves have a 5-core mains lead, white, grey, orange, blue, and earth, IIRC.
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writes:

Well that is more likely the fault then. They don't have a mid-position valve installed.
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fitted
Or more likely a divertor valve - not a mid-pos valve. Wired for dhw priority.
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Martin Angove wrote:

What you have sounds like a diverter valve instead of a mid-posn [and diverter] valve. Our beloved friends at BG had a tendancy a year or two ago to fit diverter valves heads on the 3 port valves these can only go to HW pr CH but not both. Almost nobody finds that these are a good idea. Use the main FAQ to install a "Y-plan" system. The head might be replaceable - to the mid position type. If the head is held with four screws onto the plumbing part then you will find that water issues forth as you undo screw 4.
The speed of HW production is generally limited by the heat transfer via the indirect coil and this can only be increased by replacing the HW cylinder with a modern unit which has more turns in the idirect coil.
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I thought I'd given all the info required :-) You seem to have got the idea better than the others who have replied so far. I did read the FAQ, but as for installing Y-plan (or anything else)...
Yes, it's a diverter valve, and at the moment it *does* give HW priority, but only because there is *no timer* on the HW so that whenever the system is powered up HW is produced. With power the "common" port goes to B (the coil), without power it goes to A (the radiators).
I'm perfectly happy with the diverter, but as I want to add a timer to the HW system (so you don't have to remember to flick the power on 30 minutes before having a bath - my family is lodging with my parents for a few weeks so this is very pertinent) I *can't* arrange for the valve to be permanently-powered.
As I said, the obvious solution (to me) is to physically rotate the whole diverter valve by 180 degrees. This will allow me to use the HW timer and stat to send power to the valve only when HW is required. There are not so many users of HW here that this will mean cold radiators every evening (especially after we've left and it's just mum, dad & the lodger again). As there are gate valves on all three legs of the diverter I suppose this might be possible without a drain down... but I've never done any plumbing before so perhaps you can advise.
I *think* there is a non-obvious solution utilising the SPCO contacts in the timer/HW stat/room stat and routeing power "backwards" through the system, but I'd rather not do that unless I have to.
As for switching things for a mid-position valve and installing a Y-plan, as I said, the diverter will be perfectly sufficient and I feel that this will probably add a level of complexity which isn't really required, as well as lengthening the heat-up time of the tank.
On a related subject, is there any "rule of thumb" about what constitutes a "standard" coil and a "fast recovery" coil? FWIW this (fairly recent) tank claims 0.44m2 of coil area. I presume this is "standard", but how much more would there be in a "fast recovery" cylinder?
Thanks for the help so far :-)
Hwyl!
M.
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Don't fight technology, live with it: http://www.livtech.co.uk /
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wrote:

31
live
heats
the
the
tank
the
Coil areas:
80 litre Telford Typhoon quick recovery cylinder has: 1.2 squ metres coil surface area.
120 litre Telford Typhoon quick recovery cylinder has: 1.55 squ metres coil surface area.
Both calculated to give approx 12-16 minutes recovery time.
125 litre Telford Tornado unvented cylinder has: 0.704 squ. metres coil surface area. Unvented cylinders tend to have smaller coils so as not to generate excess pressures.
From what you say it is a low performing British Standard cylinder. Quick recovery cylinders are cheaper to run.
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Martin Angove wrote:


There is no reason why you can't devise any scheme you like for controling the heating. The top principle is 1) There must be a fail safe way for the boiler to vent (assuming it is an open vented system). 2) There must be a way to ensure that the boiler is not fired when there is no flow circuit.
It is likely that the existing system meets both of these points.

Your main snag is likely to be that the gate valves are either stuck fast and/or don't shut off completely when closed.
To turn the valve around will depend on how much spring there is in the adjoining pipework, I'd need a photo to advise on the difficulty


That's about a 5 turn coil that's a modern 'standard' which is quite good enoughg to reheat the water whilst someone has a bath.
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With the diverter there will (as I understand it) always be a circuit - it's either at "A" or at "B". Only the (recently added) upstairs radiators have TRVs, downstairs do not. Otherwise so long as the pump supply comes from the same place as the boiler switched live...
[...]

Given that the pump was replaced maybe 3 years ago and the diverter is only a little older than that, I reckon I'm in with a chance. Plenty of towels to hand, eh?

There should be plenty of spring. The tank side goes for about a foot and then 90 degrees and another 6 inches into the tank, the radiator side (incidentally, the start of this circuit appears to be steel pipe - everything else is copper) goes for a foot or so then through a 90 sweep down through the floor, a drop of maybe 3 feet.
The only thing I'm concerned about is introducing 2 feet of air into the system. Yes it's fairly standard with header tank. There's a little "stub" of vertical pipe where the B leg turns 90 into the coil - this has a vent key on top. Presumably when I connect it all back together I power up the pump and open the vent until the air's gone?
[...]
Thanks for all the help so far :-)
Hwyl!
M.
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Don't fight technology, live with it: http://www.livtech.co.uk /
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Martin Angove wrote:

You vent before switching the pump back on. The air will soon find its way to a radiator.


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They are a brilliant idea with a quick recovery cylinder and the boiler to max temp. The only way to go.
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On Mon, 13 Oct 2003 22:31:17 +0100, Martin Angove wrote:

<http://content.honeywell.com/uk/homes/Catalogue/Sundial%20Plans/3.3%20W%20 Plan.pdf> Has a wiring diagram and explanation of the system, and looking at that the valve itself is the right way round at the moment.
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