Y Plan System Cabling

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Hi,

Having wired my own new central heating/ hot water system I got roped in to helping out a mate with his existing system which is round 15 years old.

It's plumbed as a y plan system with the usual mid position valve etc. His timer allows him to switch both HW and CH independently but when he switches the CH only on, the boiler does not fire unless the HW is also ON.

Initially I thought it might be a faulty mid-pos valve, but having replaced this the problem was not solved. I've now discovered that at the timer wallplate there is no cable to the HW off terminal.
This seems weird, as surely with the mid-pos valve already in place the system was designed to operate in a Y configuration, and therefore the wire should be there?
At the terminal box near the cylinder there is a spare blue wire which is simply terminated, it does not connect to anything in the terminal box, however I can't trace where this goes! The grey wire from the valve and the yellow from the cylinder stat are connected to number 7, but there is no connection on the other side of the strip. It's almost like the spare blue should go to the 7, but without this terminating back at the wall plate it makes no sense.

I suppose the question is, where could the spare blue be going to? I can't see it at the back of the stat or the controller wallplate, and if I can't trace this wire, would simply adding a wire from the number 7 terminal back down to the HW off terminal on the wallplate work?

Sorry for the convoluted question!

Cheers

Robbie
 
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Many system wirings are a botch. Bit of a nuisance, but the best way to tackle this once and for all is to check and mark every single wire at both ends, and draw a diagram of the existing situation.
Once you have that, you can compare it with the "official" y-plan diagram and the fault should be easy to spot.
Apart from finding blue or black wires actually being phase or "live", you are also likely to find "earth" wires used as live carriers. Where this is the case, the metal parts of the items connected has no earth. Although it is often done, earth or cpc's should never be used as live wires. If you can correct it, it is a good idea to do so.
 
You don't need the off wire at the clock/programmer.

I would suggest a room stat not getting or sending a signal to the valve.

Or a faulty cylinder stat.

Both easy to check with a multimeter.
 
The grey wire from the valve and the yellow from the cylinder stat are connected to number 7, but there is no connection on the other side of the strip. It's almost like the spare blue should go to the 7, but without this terminating back at the wall plate it makes no sense.

This is HW satisfied. If you connected HW off from the programmer to this, then it would be correct.
 
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right....so it's potentially correct to not have a HW off at the programmer and still be able to select heating or hot water independently? If this is the case it's the room stat that's causing the problem (which was re-wired by my mates old man when they moved in!!) If this is the case, do you know what connections should be made at the room stat?

Or......it would work fine if I linked HW satisfied back to the controller?

Cheers

Robbie

p.s Amazingly quick response by you guys....thanks!
 
Using a multi meter check the voltages in the follow places:-

CH on from programmer
To room stat
From room stat
White wire on motorised valve
Orange wire on motorised valve

All this can be done from the wiring centre easily enough and will tell us where the problem is.
 
your timer may be set for gravity hot water/pumped central heating, what is the make and model number?
 
Hi,

Thanks Elite...will meter this out over the next few days and get back to you. As I said, it's a mates system so will look when i get over there.

Hi Picasso, I can't remember off hand what it is....but I seem to remember it being an ACL Drayton? I tried moving the jumpers around on the back of the controller and it did allow me to switch the HW and CH independently, but unfortunately the room stat didn't work then....i.e when it was satisfied the boiler and pump stayed on.

Cheers

Robbie
 
The table opposite gives guidance on a quick electrical check for installed Sundial Y Plans to help in commissioning and to pin-point the source of any electrical problems.
Remember the Golden Rule when you have a problem. First of all check your wiring. Only start suspecting faulty components after you are satisfied all wiring is correct.
The following notes will help to identify faulty components.
Cylinder Stat
First of all, make sure you have wired to the correct terminals.
Terminal C (common) is the Left Hand terminal.
Terminal 1 is the Middle terminal.
Terminal 2 is the Right Hand terminal.
Suspect the cylinder thermostat is faulty only if Terminal 1 does not become live when calling for Hot Water, or Terminal 2 does not become live when satisfied. (Make sure that Terminal C is live in both cases). While checking, disconnect Terminals 1 and 2 to prevent false readings due to backfeed.
Room Stat
1) Remove wire from Terminal 3.
2) Live to Terminal 1.
3) Turn stat to call, if no live on 3 then faulty.
Suspect the room stat is faulty only if Terminal 3 is not live when calling for heat. (Make sure Terminal 1 is live). While checking, disconnect wiring from Terminal 3 to prevent false readings due to backfeed.
Mid-Position Valve
Suspect the V4073A valve is faulty only if the valve does not operate as specified in the following checks (these should be done in order 1, 2, 3, 4, 5 and 6).
Valve open for Heating only
1. Switch off mains supply. Disconnect Grey and White wires from appropriate junction box terminals. Reconnect both Grey and White wires to permanent live terminal in junction box.
2. Switch on mains supply. Valve motor should now move to fully open heating Port A. The motor should stop automatically when Port A is open, and stay in this position as long as power is applied to White and Grey wires. When Port A is fully open, the Orange wire becomes live, to start pump and boiler.
Double check by feeling that Port A outlet is getting progressively warmer.
Valve open for D.H.W. only
3. Switch off mains supply. The valve should now automatically return to open D.H.W. Port B and close Heating Port A.
4. Isolate Grey and White wires and make safe.
Remove cylinder stat wire from Terminal 6 in junction box and connect to permanent live. Switch on fused spur, cylinder thermostat must be set to call for heat, pump and boiler should start.
Valve open for both D.H.W. and Heating
5. Switch off mains supply. Replace cylinder stat wire to Terminal 6. Isolate and make safe Grey wire and connect White wire to permanent live. Switch on mains supply, motor should now move to mid-position and stop automatically. Cylinder thermostat must be set to call for heat. Both ports A & B are now open for Hot Water and Heating. Boiler and pump should start.
Double check by feeling that pipe outlets from ports A & B become progressively warmer.
6. Switch off mains supply, reconnect White and
Grey wires to junction box terminals.
If this check completes satisfactorily, the problem is not the valve, but elsewhere in the circuit.
Programmer
Suspect the programmer only:
(a) After you have made sure that any links
required are in place,
(b) After you have made sure that the Programmer has power – to the correct terminal,
(c) After you have made sure that the Programmer timing is set up correctly (see individual Programmer User Guide as appropriate),
(d) If live does not appear at Heating ON Terminal when Heating only is selected on continuous or timed,
(e) If live does not appear at Hot Water ON
Terminal when Hot Water only is selected on
continuous or timed,
(f) If live does not appear on Hot Water OFF terminal with Hot Water OFF on programmer
 
Thanks for the advice Doitall,

I think, should testing the roomstat not provide any answers, and wiring a single down to the HWoff pin on the controller not solve it I'll just rip it all out and re-wire myself, it would be quicker!

Cheers

Rob
 
Hi Guys,

OK, the wiring was a mess, so I totally re-wired the wiring centre and belled out all the cables to check where they were going. I've re-wired exactly as specified on the wiring diagram that comes with the valve other than having the DHW off wire going to the programmer. I still can't select heating only, assuming this is due to the lack of DHW off wire is there anyway I can wire it so we don't require this cable back to the programmer?

Cheers

Rob
 
Hi Guys,

OK, the wiring was a mess, so I totally re-wired the wiring centre and belled out all the cables to check where they were going. I've re-wired exactly as specified on the wiring diagram that comes with the valve other than having the DHW off wire going to the programmer. I still can't select heating only, assuming this is due to the lack of DHW off wire is there anyway I can wire it so we don't require this cable back to the programmer?

Cheers

Rob
Would it be so difficult to rewire programmer?
if so you could use a relay to provide 240 to grey when hw switched off
or you could convert to s-plan(more expensive)
 
Hi Matt,

Yeah, getting the extra cable back to the programmer would be a nightmare, it's my mates house and he's just had new carpets fitted etc. Seriously big job.

How would the relay solution work??

Cheers

Rob
 
Hi Matt,

Yeah, getting the extra cable back to the programmer would be a nightmare, it's my mates house and he's just had new carpets fitted etc. Seriously big job.

How would the relay solution work??

Cheers

Rob

sorry haven't got time to to work out how to do a drawing and don't know what you have in the way of wiring centre but basically
you could use a 230v single pole double throw relay wired as such:
wire the coil to hot water on (and neutral of course)
wire the NC contact to gray and provide permanent 230v to the relay common
basically your are providing 230v permanently to the grey via the relay.when you select hW the relay will energise and remove said voltage from the grey, the cylinder stat will then provide grey with 230v when satisfied (if you have wired stat correctly)
if you are really stuck picking up a permanent live,(one that can be isolated together with the other boiler controls ie on the same circuit) then connect relay common to the white wire (this will work but not ideal as connecting to white will mean the valve will power down and motor back up every time room stat is satisfied/calling so you will get some circulation in the hot water circuit while pump is over running)
hope I have explained ok I'm sure someone else on the site will provide a drawing to explain better
matt
 

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