Central heating and hot water problem (possibly mid position valve related)

[jackthom]

Can you restore the cylinder stat wire to where it was and this time remove the Orange wire to see whether the Live is coming from the valve (maybe use an unconnected terminal on the main block such as #5 to safely anchor it).

Measure voltage of seperated orange and then the terminal it was connected to.

If Orange is still 240V quickly check the voltages of the other wires to the valve, Grey & White.

 

[rgl-1980]

No reading from the orange wire once it has been connected to #5 (no reading from white or grey now either)

Terminal it was connected to is reading 240v

 

[jackthom]

OK pop the orange and the other wire (is it a dark brown to pump?) that was in with it back together where they were.

Now you'll need to separate out the yellow and blue wires from that terminal and place each of them into unused positions so you can confirm which one is providing the live.

Then identify where in the system that live wire is coming from.

A bit hard to tell from the photo in the first post but do both the yellow and blue come from one cable ???

 

[rgl-1980]

Orange and dark brown which goes to the pump, yes.

Yellow and blue are now in separate terminals. No reading on blue, 240v on yellow.

Those two wires are not from the same cable. The blue one is from the cylinder stat and the yellow one is from the grey cable that goes through the floor boards

 

[jackthom]

So that cable carrying the yellow might be a permanent live from the boiler?

 

[rgl-1980]

Yes, it seems the yellow is permanent live from the boiler.

I've now connected the blue wire from the stat with the Orange wire from actuator and brown wire from pump. Yellow wire is temporarily isolated, away from the others. I've put the programmer back on the back plate.

With CH only selected, the pump comes on, the boiler fires and the radiators are getting warm. I have 240v on Orange, grey and white.

With CH off the pump stops and the boiler goes off. There's now no reading on Orange or white, 240v on grey.

With HW only selected, the actuator moves to W, the pumps starts but the boiler does not fire. I have 240v on Orange, about 30v on white and a very small reading on grey.

With CH and HW both on, the actuator moves to the mid position, the pump and boiler start up. Orange is 240v, white is 240v, grey is around 120v.

With HW on the loose black wire (which is coming from the cylinder stat cable) gives a tiny reading (the needle on multimeter barely moves. With HW off, no reading. With CH on the black wire gives a tiny reading and no reading when off. With CH and HW both on, again I get a tiny reading on the loose black wire.

 

[jackthom]

I think you're nearly sorted with this. It looks like the cylinder stat wiring is preventing hot water from working but the heating side is ok.

There should be three wires going to the stat from the wiring centre.
One takes HW ON from programmer to the stat common.
One returns this live signal to the terminal carrying orange/pump/boiler while the water is below temp.
The third joins up with the HW OFF and grey wire to signal HW OFF when the water is up to temp in the cylinder.

I would first use the meter to identify the HW ON wire from programmer and see where that connects to the cyl stat. Post a pic of the actual cylinder stat wiring at the far end if you can.

 

[rgl-1980]

Ok, I'll check on that. I'll probably go back to this at the weekend as I'm back at work today.

Really appreciate your help with this and now feeling a lot less stressed!

 

[stem]

Just to go back to the wire that isn't connected to anything. I have studied your photographs and as best as I can see it looks that there is only one wire connected to the motorised valves grey wire.

Based on how a Y plan should be wired, and from what I can see in your photograph, I have put together a drawing showing how I believe it is connected. If my drawing is correct, then the 'spurous' wire I believe is the 'hot water satisfied (or not required)' signal from the cylinder thermostat, which should also go to the grey wire on the motorised valve, (X marks the break) along with the red sleeved wire which is the 'hot water satisfied (or not required)' signal from the programmer.

I have assumed that you don't have a room thermostat as it's not wired back to the terminal box, but it may be connected as a switch into the circuit elsewhere.

Please check that your wiring does correspond with what I have drawn, before connecting the wire. It is difficult to see all of the wires in detail and of course the boiler and cylinder thermostat details have not been provided and are assumptions.

 

[jackthom]

hi stem, thanks for the diagram which is useful. What's still baffling me is how the system is functioning at all now the yellow is ditched. I had thought red must be the Live supply, linked through to the programmer via terminal 14 (is that wire black or brown?) .

I can't yet get my head around how the boiler is getting it's demand signal. Most people wiring it would have used the yellow.

rgi-1980... Some pictures of wiring at the boiler end would be very useful.

 

[stem]

I was just scrutinising the wiring colours, it's difficult for me to tell from the photo what is black and brown, is this better? More important is what terminal is connected to what terminal rather than the actual colours used.



Terminal 14 I believe is just used a permanent live connection. The mains live supply from the boiler (red) is then connected to the live going to the programmer (brown)

I will give the "demand signal" some more thought when I can focus a bit more. It is an odd fault and I'm wondering if there is more than one problem at play here. If rgi-1980 could confirm at some point that the wires do go to the terminals as I have shown them and that there are no other connections anywhere, that would be helpful.

 

[rgl-1980]

@stem I will add some better photos over the weekend to make things clearer, but you are correct that the grey wire is currently only connected to one other: the red sleeved wire from the programmer

And there's no room stat, as you suspected.

 

[stem]

There is something odd here, and that relates to the yellow wire which you say shows 240v when it is disconnected from the other wiring. I would not expect to see any voltage there. Bear with me on this as I'm not too good explaining things in writing, but I will have a go.

In installations like yours, the yellow wire would normally be used as a 'switched live' to the boiler, and indeed, based on that assumption, your photographs show exactly what I would expect to see, as follows:

1. The yellow wire is connected to the orange wire from the motorised valve. The orange wire is made live by the valve when it winds to the H position and provides the 'on' signal to the boiler via the yellow wire when heating only is required.

2. The yellow wire would also be connected to the cylinder thermostat, so that when hot water was required the cylinder thermostat can also start the boiler.
This is what I see in your photos and is exactly what I would expect.



So far so good. However, in your case:

Yellow wire is temporarily isolated......With CH only selected, the pump comes on, the boiler fires and the radiators are getting warm.

The boiler should not be running with its switched live disconnected, but it would appear that it is. Are you really sure that the boiler actually fired up, or was the pump just circulating already hot water it contained? [The pump would still run if it was still connected to the motorised valves orange wire.]

This raises the following questions.

1. Why is the boiler running when the switched live supply appears to be disconnected?
2. Where is the 240v on the yellow coming from?
3. Is the yellow actually being used as the boilers switched live? if not what is?

When you get chance, can you confirm that my last sketch shows the wires from terminal to terminal as they are actually connected, and can you find the other end of the yellow wire and tell us what it is connected to or post a photograph please.

Apart from you changing the motorised valve innards when the problem occurred, has anything else been changed?

 

[rgl-1980]

The boiler should not be running with its switched live disconnected, but it would appear that it is. Are you really sure that the boiler actually fired up, or was the pump just circulating already hot water it contained? [The pump would still run if it was still connected to the motorised valves orange wire.]

The boiler is in the garage, so I didn't actually go into the garage and see that the pilot light was lit, I just heard, or thought I heard it start and I then stuck my head out of the bathroom window, which is above the flue, and I could smell the flue and hear it extracting. So I'm pretty sure the boiler was firing, but I will double check on this point.

I was also expecting the yellow to be switched live, so I was surprised that the heating came on. There was barely any hot water in the tank as the power to the boiler had been switched off for a couple of days before I went back to check the wiring yesterday. So again, I don't think it was already hot water going to the rads.

I'm going to mention something at this point which I didn't think was relevant when I first posted, as I thought the problem was related to the three port vale and actuator, but it seems relevant now we're getting into the wiring. The boiler was serviced and safety checked before this problem started, but I thought that was a red herring/coincidence, especially given that one of the legs on one of the resistors had come away from the circuit board in the actuator and there was definitely a problem there. I can't think why they would have fiddled with the boiler wiring, but if the live and switched live at the boiler end were the wrong way round, could this be the cause of problem? I'm just thinking out loud here as I'm not qualified, so this could be totally wrong, but as I say, it could now be relevant.

 

[stem]

I wondered about that, but if they were swapped around, then the boiler would run continually 24/7 and you would have the same problem with the hot water as you do with the central heating. Having said that, it's looking more and more likely that this could be where the problem is. Lets see what you uncover when you have a look at the boiler wiring terminals. From the photo of the motorised valve terminals, I can't see a live supply from a fused spur, so I've assumed that it's fed in from the boiler via the grey sheathed cable, so hopefully you should find the main supply at the boiler end as well.

BTW my theory about the disconnected wire wouldn't cause this. All that would do, would be to keep the hot water running if the HW was 'on' at the programmer and 'off' at the thermostat, but only when the central heating was running at the same time. You would just notice that the hot water was hotter than usual when the heating was on.