Yes, I understand. I was not allowing for when the HW On signal comes from programmer, but the tank stat remains open (i.e. tank up to temperature). In this situation the CH wouldn't have worked if asked for.
Thanks again, all now understood.
Luke
On second thoughts Set Square I'm not convinced.
You suggest wiring the 2-way valve's Common terminal to HW On from the programmer. Let us imagine the tank stat is Closed (i.e. below temperature), but the programmer says HW off and CH off.
In this scenario Grey to the 3-way valve is live (fed by HW Off from the programmer), which is also connected to the White wire of the 2-way valve. White is connected to Common (Orange) when the 2-way valve is closed.
Unfortunately this means the Common terminal now becomes live and, because Common is connected to HW On, if the Tank Stat is closed, the
2-way valve now starts opening, fed by the orange Common wire. As the valve opens, Orange and White are no longer connected, breaking the feed to the 2-way valve, and it shuts again. Therefore restoring the connection between Orange and White. Then it starts opening again... and so on..I've just drawn a circuit diagram and can envisage this happening. I could post it if need be.
Luke
On second thoughts Set Square I'm not convinced.
You suggest wiring the 2-way valve's Common terminal to HW On from the programmer. Let us imagine the tank stat is Closed (i.e. below temperature), but the programmer says HW off and CH off.
In this scenario Grey to the 3-way valve is live (fed by HW Off from the programmer), which is also connected to the White wire of the 2-way valve. White is connected to Common (Orange) when the 2-way valve is closed.
Unfortunately this means the Common terminal now becomes live and, because Common is connected to HW On, if the Tank Stat is closed, the
2-way valve now starts opening, fed by the orange Common wire. As the valve opens, Orange and White are no longer connected, breaking the feed to the 2-way valve, and it shuts again. Therefore restoring the connection between Orange and White. Then it starts opening again... and so on..I've just drawn a circuit diagram and can envisage this happening. I could post it if need be.
Luke
I don't *think* I'm wrong. Would you like to upload your diagram somewhere, and post a link to it?
If the original stat drives the valve, the valve's volt-free contacts will always be in the same state as the cyl stat contacts (give or take a few seconds for the valve to open or close). So if you connect the volt-free contacts to whatever the cyl stat contacts were previously connected to, the
3-way valve won't know the difference.
I've created a picture in Word and put it here, I hope this is okay:
This is the problem as I see it:
In the diagram the situation at the moment is CH off, HW off. Grey wire to 3-way is live fed by HW Off from the programmer. Grey wire is also connected to 2-way valve as shown. Tank Stat is closed (ie Water too cold). 2-way valve is closed. 3-way valve is in rest mode meaning Orange wire is not live.
When 2-way valve is closed (as shown), this completes the circuit from Grey wire (HW Off) to the Yellow wire (Hw on). If the tank stat is closed (i.e. water too cold), this in turn makes the green wire between Tank Stat and 2-way valve live. CRUCIALLY, now the 2-way valve begins to open but, as the microswitch makes its way from the Grey to the Orange wire, the circuit is broken, meaning the valve shuts, connecting Grey to Yellow once more... opening the two way valve again...
I hope this makes sense, thanks for reading.
Luke
I need to know what type of boiler you have as this dictates wha system requirements you need...anyway i would guess that your 3 way mi pos valve is passing and some silly person has simply added a 2 por valve in series with your hw circuit...ok it works but its untidy an daft...no overheat stats bring on pumps....its called a pump overru stat...would recommend replacing your zone valves with s pla configuration ....install a bypass if needed of wante
-- gastec
Yes, I understand what you're saying. Under some circumstances with a conventional Y-Plan system, the HW-off signal feeds back through the cyl stat and makes the HW-on live - but only when the stat is in the satisfied condition - so it doesn't do anything.
The difference here is that, contrary to what I said earlier, the volt-free contacts on the 2-port valve *don't* exactly mimic the cyl stat - so you can have a situation where the switch on the 2-port valve is in the 'satisfied' position whilst the cyl stat is in the calling for heat position. This will only happen when HW is turned off at the programmer, but is still a *real* situation.
It's doing my brain in, trying to work out the solution. It *may* be (but I'm not yet 100% sure) that you have to connect the 3-port valve grey wire to the satisfied contact on the cyl stat rather than to the equivalent point in the 2-port valve. What do you reckon?
Exactly.
rt valve grey wire
int in the 2-port valve. What do you >reckon?
Do you know I think you've cracked it! I've done a new circuit diagram:
To other contributors, I agree it would be perhaps easier from a wiring perspective to convert to S-Plan but that would cost me =A370 for 2 additional motorised valves as well as the cost of the bypass valve and this way I'll only have to buy a bypass valve (=A325).
Boiler by the way is a Potterton Prima F so no doubt I'll be needing a new circuit board from Geoff before too long!
I beg your pardon gastec I had my terminology confused. By Overheat Stat I did of course mean Pump Overrun Stat.=20
Thanks again to all Luke
In the normal Y-plan layout the HW off signal from the programmer and the HW satisfied signal from the tank stat are joined together and go to the grey wire on the three port.
In this arrangement the white wire on the 2-port valve will have the exact same effect as in the traditional layout - namely either HW is off or HW is done.
So to make things explicit:
2 port Brown from HW program via tank stat. Orange to 230V line. White to grey on 3 port. Grey to orange on three port and boiler demand.3 port White from CH program via room stat. Orange to boiler demand and grey on two port. Grey from white on 2 port
Incidentally does anyone know if "white wire" 2-port valve is normally supplied with an unvented cylinder?
Good - I thought it was looking hopeful, when I printed and marked up your previous diagram. Sorry about the earlier info - it's the first time I've come across this setup!
Ed,
Looks like this would also work.
I think I will however use Set Square's latest plan
Luke
valve grey wire
in the 2-port valve. What do you >reckon?
You'd only need one extra 2 port valve as you already have the one needed for the cylinder in place! (There is no requirement to use TWO 2-port valve on the indirect circuit.)
It's not a Suprima it's an older type which is quite similar to a Profile in many ways. The Profile is a reasonable if somewhat dated bit of kit.
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