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

[jackthom]

I'm wondering if both yellow and red have become permanent Live, possibly by coming into contact with each other in the boiler wiring.

The boiler may then have been permanently receiving demand and sitting at a high temperature, only stiopped from firing continually by it's own internal thermostat.

Unless it was checked regularly in the garage you would only hear the pump switching off and assume the boiler had also been stopped.

 

[rgl-1980]

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.

In my initial post I said that the central heating was permanently on, but it's possible that the hot water was also permanently on (I didn't check) and I had wrongly assumed that it was only the central heating that was stuck on (as the actuator was stuck on H regardless of what the programmer was set to). When I replaced the actuator, the central heating went off when the actuator moved to the the W position and hot water was then being permanently requested, despite the programmer being off

 

[rgl-1980]

I'm wondering if both yellow and red have become permanent Live, possibly by coming into contact with each other in the boiler wiring.

The boiler may then have been permanently receiving demand and sitting at a high temperature, only stiopped from firing continually by it's own internal thermostat.

I shall try to get to the boiler wiring at the weekend.

 

[stem]

It's possible that both yellow and red have become permanently live. If it's an older boiler (and I don't think the OP has said what type it is) it may not need a permanent live, but there must be one there because it's linked out to the programmer as its live supply. The fact that the pump is wired to the motorised valve terminal box suggests the boiler is not fitted with a pump overrun which would need a permanent live. So maybe the wires have been inadvertently put in one terminal, or if it has a plug connector, it has not been inserted properly.

It would certainly explain how the white wire was staying 'live' when the central heating was 'off' at the programmer. It would be getting a supply through the motorised valves internal microswitch from the orange wire, from the yellow from the boiler. The hot water off signal (grey wire) would keep the valves motor in the central heating position and thus the microswitch closed. It all seems to fit.

Methinks we are making some progress.

 

[rgl-1980]

It's an Ideal Classic which I would guess is 20 years old. I'll check exactly which model when I'm home

 

[stem]

It probably doesn't need a permanent live then, but best for you to check.

If it doesn't, the incoming 'live' from the fused spur should only be connected to the red wire going to terminal 14 at the junction box. The boilers 'live' supply would then be the yellow wire coming back from the junction box.

 

[Johnmdc]

Is there a frost stat in the garage near the boiler maybe this is what's making the yellow wire live. If there is check what it is set at.

 

[rgl-1980]

@stem

View attachment 88506

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.

The wires are as shown in your diagram

 

[rgl-1980]

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.

View attachment 88509

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?

Have now double checked and the boiler fires when CH is turned on at the programmer despite the yellow wire being isolated.

Nothing has been changed apart from the motorised valve innards

 

[rgl-1980]

@Johnmdc

Is there a frost stat in the garage near the boiler maybe this is what's making the yellow wire live. If there is check what it is set at.

This is connected to the boiler in the garage. I've never noticed nor touched this before. My photo shows it set to 60.

I turned this down to 20 and noticed there's no voltage going to the yellow wire. Turned it back up to 60 and get 240v on yellow wire.

So that's what the yellow wire seems to be connected to.

 

[rgl-1980]

It's an Ideal Classic which I would guess is 20 years old. I'll check exactly which model when I'm home

Can't see a model number apart what's shown here

 

[rgl-1980]

I've wired things back up as they should be and turned the stat in the garage right down and everything seems to be working as it should be.

So I'm guessing when the boiler was being checked they turned that stat right up to keep it running and forgot to turn it back down. Then, completely coincidentally, I had a problem with the valve and a loose wire, which confused matters.

Thanks for everybodys' input and time on this and sorry it was a bit of a wild goose chase. I do feel like I've learnt something though

 

[Johnmdc]

What did you do with that loose black wire that wasn't connected it should go to the grey wire from the valve. If it isn't connected and you have water and heating switched on once the water is up to temperature the heating will also go off.

 

[rgl-1980]

I connected it to the grey wire

 

[stem]

Thanks for posting back, It's always good for us to find out the end result, so we can learn too.

It's a bit of an unusual way to wire a frost thermostat. Normally there is an air thermostat to sense when the air temperature falls below 5 degrees and turn the boiler on. This is then wired in series with a pipe thermostat on the boiler return pipe that turns it off again when the circulating water temp reaches 20. Probably yours was a later addition and wired directly across the boiler terminals for ease.

If you only have the pipe thermostat, when the temperature of the pipe falls below that, the system will switch on, which in a garage (unless it is very well insulated) I would imagine would be fairly frequently, so I'm surprised that in 13 years you've not noticed it coming on in the middle of the night before. Anyway well done to johnmdc for spotting it. It did cross my mind briefly, but I discounted it because there was no sign of it wired into the junction box, and I've never seen one directly wired across the boiler terminals. Also, at the time the weather wasn't anywhere near cold enough for a frost thermostat to cut in. Unlike today

It's not dangerous or anything, so there's no need to change it if it's not causing a problem. However, I do think you should inform the person who serviced your boiler what's happened, so they can learn too. It's a bit of a schoolboy error.