Controlling hot water and heating separately

[IanJg]

Hi, looking for some information.

I have what is probably a fairly standard set-up for central heating and gravity fed hot water with what I think is a Y-Plan design. What I want to know is if it is possible to control the hot water and heating separately?

At the moment if we turn the heating on via the ST9400C controller it also turns the hot water on. We can just switch the hot water on it's own but cannot switch the heating on on it's own. Is there a relatively simple way to change this or is it just not possible?

The system appears to be using a Honeywell V4073A1039 3 position valve and looking around on the internet it kind of implies that it should be possible to use this valve in a way that makes the above achievable or is that just wishful thinking on my part?

 

[45yearsagasman]

Your 9400c should be able to control ch and hw independently providing your system is wired up correctly as a y plan.

 

[IanJg]

Your 9400c should be able to control ch and hw independently providing your system is wired up correctly as a y plan.

Well that gives me hope Pete, thanks. I guess the thing that may stop me is if the number of wires going from the controller to the wiring box by the motorised 3 way valve then? If memory serves I think there are only 3 wires and it may need 4?
Time to do some investigating.

 

[45yearsagasman]

If your programmer and wiring centre are near the 3 port valve, pump, and cylinder with its cylinder stat, then it should be fairly simple to sort your wiring out. You will need a multimeter and an understanding of y plan wiring. You don't say what boiler you have?

 

[IanJg]

If your programmer and wiring centre are near the 3 port valve, pump, and cylinder with its cylinder stat, then it should be fairly simple to sort your wiring out. You will need a multimeter and an understanding of y plan wiring. You don't say what boiler you have?

Unfortunately the programmer is in the kitchen, just about as far away from the wiring centre, the pump and the valve is it is possible to be in this house. The pump and the valve are in the airing cupboard with the hot water cylinder and the wiring centre is in the wall and will take quite a bit of pfaffing around to work out which wires come from the programmer, the single house thermostat in the hall and which goes to the boiler. I presume if it's wired right (I think it wouldn't work if not) then the orange wire (heating only) should be connected to 3 other wires which looks right even if the colours of those 3 wires are confusing, 1 red, 1 brown and one black. Hopefully the black is switched live from the cylinder stat which annoyingly doesn't have a red or brown sheath and the other two are the live to the pump and boiler. That's all guess work though as I haven't confirmed all of them yet.

Not sure if knowing the boiler will help much, it's an Ideal iCos HE18, I know they don't have the greatest reputation.

I did do a lot of reading last night after your post to try and work out how to convert to independent HW and CH and discovered that the ST9400C is configured in mini-program mode which explains why HW always comes on when CH is switched to on. Seems easy enough to change but don't want to do that until I can confirm the way things are wired up will allow it to work. It may be that way as it's the only way it will work because the old programmer used to be an ST699B but not sure of that.

Looking at some Y-Plan wiring diagrams online and a few posted here, there seems to be no wire for CH Off which is confusing me a lot. I thought it would need HW on/off and CH on/off wired up in the programmer but maybe not.

I have had the plate of the wiring centre box and it's doesn't exactly inspire me the the house builders were that good as it appears to be a 2 gang galvanised back box, 10 block of 15A connector blocks with a blanking plate over it with a sticker on saying do not remove without isolating the system first Hey maybe that was what the norm was in 1990 when this house was built but seems a bit Heath Robinson and corner cutting.

I realise I have mentioned a lot of colours and wires and it's going to be confusing as hell to work anything out from that, so even though I am a bit embarrassed that the attached wiring is in my house a picture will definitely be worth a thousand words here so I will attempt to attach it below. Please be kind I didn't wire it like this the builders did.

 

[45yearsagasman]

Ian, my eyes hurt trying to figure that wiring centre. I would recommend getting a heating repair guy round to trace and rewire your system. Doing it from behind a keyboard is to be honest, very difficult. For a yplan to operate as designed it should have a hw off connection at the programmer.View media item 30560This diagram may assist.

 

[IanJg]

Hi Pete, yeah I spent 30 mins or more trying to work out what the wires in their did. As I said the builders need shooting, I have never needed to look in there before. At some point I think a really good tidying up inside that box would not hurt but not now as we head into winter...

One question: Am I right that the programmer/timer doesn't need a wire to CH OFF to be able to control the HW and CH independently?

I have identified all the wires now so do know roughly how the power will flow around the wires I have. A couple of the wires surprised me as they didn't go where I thought which was causing confusion when looking at the wiring diagrams but now I have the wires identified correctly things make a lot more sense. Biggest problem now is I cannot work out how to get the ST9400C front off... will work that out and see how it is wired up but I know it is using triple and earth wire (with the old red, blue and yellow colour scheme) so there are definitely only 3 connections and one of them is the neutral so things are going to be tricky I expect as I am betting the HW OFF wire is missing It's annoying that the neutral from the programmer/timer is probably the only neutral as the blue wire in the triple and earth would be available but since the 13 amp fused spare is next to the controller it has to be there

And thanks again for your help.

 

[45yearsagasman]

Am I right that the programmer/timer doesn't need a wire to CH OFF to be able to control the HW and CH independently?

Quite correct. Heat On, HW On, HW OFF is all you need.

 

[Echo the husky]

There certainly doesn't appear to be a HW off from the programmer, just one from the cyl stat. Without it the valve can't move from the mid position to CH only.

Edit: your programmer has 2 screws underneath, Turn power off, loosen the 2 screws, then the programmer hinges up and off.

 

[Echo the husky]

If you have a permanent live in the wiring centre you posted, it is possible to fit a changeover relay to get hw on and off, to save installing another cable. However many y plan heating systems have no permanent live at the wiring centre.

 

[IanJg]

If you have a permanent live in the wiring centre you posted, it is possible to fit a changeover relay to get hw on and off, to save installing another cable. However many y plan heating systems have no permanent live at the wiring centre.

Unfortunately not. Because the switched fuse is next to the programmer they didn't bother putting a twin and earth into the wiring centre as well as the triple and earth. That one extra cable to carry live, neutral and earth would mean there would technically be enough wires even if one of them would be an unsheathed earth for one of the CH/HW on or off's. Not something I would think is allowed anyway.

The ultimate goal for wanting to know if it was possible is I have been looking at smart heating options and as far as I can tell all of them just want to replace the programmer but none of them seem to be able to cope with HW & CH tied to each other. Which when you think about it you wouldn't want anyway as it defeats the main purpose of them.

Can't believe for the sake of £2 of cable the builders didn't make the two systems independent.

Thanks for looking at this anyway.

 

[Echo the husky]

even if one of them would be an unsheathed earth for one of the CH/HW on or off's. Not something I would think is allowed anyway.

Absolutely not allowed!!

Improperly wired central heating systems are very, very common, just look at some of the threads here. Many electricians don't understand how they work and many plumbers don't have a clue.

 

[IanJg]

Maybe I am looking at this all wrong. Ultimately if I get everything relocated to the airing cupboard where the wiring centre is it just becomes an issue of how to get a live, neutral and earth to the programmer or it's replacement in the airing cupboard.

Only problem then is we lose the easy visual status of the CH and HW. However just about every smart heating system replaces the room stat with something to show temperature and/or controller which might be enough.

 

[Echo the husky]

If you move the programmer to the airing cupboard the cable that currently does heating and hotwater will become the mains supply.

 

[IanJg]

Wouldn't it need a double pole fused switch in the airing cupboard with 3 amp fuse though? Where the programmer is now would have to become a junction box to connect the supply from the fused switch next to it to the one in the airing cupboard which would mean there would be two fuses in that run. I suppose if the first was 13 amp and the one in the airing cupboard was 3 amp then it would go first if there was ever a problem. Would that be allowed? and who better to ask a heating engineer or an electrician?