No power getting to a Baxi boiler

[Pearlyman]

I have recently taken down a partition wall that was in my utility room, as part of some work that has been carried out in the area. In addition to some 13A outlets, the main power supply switch and the timer for the central heating both resided on the wall (it is adjacent to the wall where the boiler is located).

A new wall was put up in the same place, the following day and all of the electrics re-instated exactly as they were – or so I thought…

At the beginning of this week, I reconnected the power supply and whilst all the 13A sockets worked fine; no power was reaching the boiler (suggesting that I have either wired up the central heating power supply switch, or the timer incorrectly).

I took photographs of both boxes before they were disconnected – and I was sure I had put back all of the wires in the same place – but it would appear not…

Power is getting to the central heating power supply switch (the neon light glows when it is switched on) – and indeed to the timer switch next to it (the clock on it lights up and the red lights showing heat/water on, work as expected).
However, there appears to be no power getting from the timer switch to the boiler (it’s green power light isn’t glowing).

I called out a British Gas engineer yesterday, in case something just needed resetting or had fused on the boiler.
He went upstairs and manually moved one of the valve switches in the airing cupboard in the hope it might trigger some activity. Instead, it blew the 5A fuse in the central heating power supply switch.
At that point he left the house and told me I needed an electrician !

I am trying to get hold of a suitable electrician – but they aren’t that easy to find.
I realise that this problem is probably too complex to enable resolution via a forum – but I thought it worth raising in case anyone had any ideas of what the issue might be (I suspect I’ve just made a small mistake somewhere).
Details of the central heating power supply switch/timer/boiler are as follows:


Central Heating Power Supply switch

5 cables coming in: 2 for the ring main; a link to the room stat; a link to the timer; and a link to the airing cupboard (where the pump, motorised valves etc are located).
There is also a single core yellow which I think links the earth in the switch with the earth in the timer.

The switch is wired up as follows:

N load - Blue (room stat) and blue (timer)
N feed - Blue ring main x 2
L load - Red (room stat) and brown (timer)
L feed - Brown ring main x 2
Earth - Earth ring main x 2, earth (room stat), single earth wire (timer ?)

Connection block linking red (airing cupboard) with black (timer)
Connection block linking blue (airing cupboard) with yellow/green (timer)
Connection block linking yellow (airing cupboard) with black (timer)

Timer – Honeywell ST6400C

Has a cable coming in from the central heating power supply switch and a cable going out to the boiler - plus a single yellow wire which goes to the earth terminal.
There are 7 terminals where wires are connected – plus a connection block.

1. Earth - Single yellow wire (CH power supply switch ?)
2. Neutral - Brown (CH power supply switch)
3. Live - Blue (CH power supply switch) and blue (boiler)
4. HW Off - Nothing
5. CH Off - Nothing
6. HW On - Black (CH power supply switch) and brown (boiler)
7. CH On - Black (CH power supply switch)

Connection block linking yellow/green (CH power supply switch) and yellow/green (boiler)

Boiler – Baxi 100 HE

I believe that this is exactly how it was all wired up before I took the boxes off the wall (I took photos and made notes).

The only mistake I felt I might have made was with the black wires in the CH power supply switch – but I changed them round and it made no difference.

I’m a little puzzled as to why the Live and neutral in the timer are wired the way they are – but that is how it was (and I have photographic evidence to prove it !).

All thoughts/suggestions/comments very welcome !!

 

[EFLImpudence]

Well, presumably (obviously) the live and neutral at the timer are the wrong way round but if you say that's how it was I cannot argue.

Have you swapped wires somewhere else that would normally be correct but because of the timer wiring would now cause a fault?

Can you post your pictures?

 

[Pearlyman]

Hi EFL,
Many thanks for the reply.

You helped me out a couple of years ago when I had a similar (though slightly simpler !) problem with an extractor fan - and I was very grateful then as well !

I've uploaded 4 images below: 1 of the room stat (which is very simple); 2 of the CH power supply switch (though it is not easy to make out all of the detail) and 1 of the timer (slightly blurred - but not as complicated as the power supply switch).

I also did a drawing of the timer wiring - and used different coloured insulation tape to try to ensure I replicated what was previously there in the power supply switch...

I've changed nothing else (other than the ring main wiring - but that works fine). I was simply trying to put back everything as it was.

The only change I've tried is with the black wires in the power supply switch. I thought I had them the right way round - but I couldn't be adamant.

The only other thing I think that I could possibly have got wrong, is mixing up the room stat cable and the cable to the airing cupboard ! I'm 99% sure I didn't, as I put insulation tape on the airing cupboard cable to identify it - however, superficially the cable looks exactly the same (grey sheathing, 4 wires, blue, red, yellow and copper).

It really is a mystery to me - but I've obviously got something wrong !

View media item 66613 View media item 66614 View media item 66615 View media item 66616

 

[EFLImpudence]

I can't really make sense of your connection list.

For example
from timer
"HW On - Black (CH power supply switch) and brown (boiler)"
and from switch
"L load - Red (room stat) and brown (timer)

I don't see how it can or could work properly.

Are you certain of the description or are you assuming the wires of the same colour are the same one.


I think the only solution is to start again.

What system do you have?
Two two-port valves or one three-port valve.

 

[EFLImpudence]

And do you have a wiring centre box?

 

[Pearlyman]

When you say that you can't make sense of the connection list, do you mean that you are struggling with my description - or do you understand my description but are struggling to understand how it ever worked ?

I assume the latter, but just in case:
Taking the timer connection that you question as an example; what I am saying is that there is a connection on the timer switch, which is labelled 'HW On'. There are 2 wires going in to it: a black, which originates from the CH power supply switch; and a brown which is going to the boiler.

If you look at the picture of the wiring for the timer switch, it is the connection one in from the right. You can see the brown wire going down in the cable that goes to the boiler; and there is also a partially hidden black behind it, which goes back to the power supply switch (the power supply switch and the timer sit right next door to each other)

I’m pretty sure of my description of each cable/wire.
If you ignore the ring main, there are only 3 cables going into the switch: one from the room stat; one to the airing cupboard and one to the timer.
I’m 100% sure of the link from the power supply switch to the timer (the cable is a different colour) and 99% sure that I have correctly differentiated between the cable form the power supply switch to the room stat and the one to the airing cupboard…

I think that I have 2 X 2-port valves and I think that I have a wiring box – and I believe that they are all located in the airing cupboard (I’m not a central heating expert though !)

 

[EFLImpudence]

When you say that you can't make sense of the connection list, do you mean that you are struggling with my description - or do you understand my description but are struggling to understand how it ever worked ?

I assume the latter, but just in case:

Yes, the latter

Taking the timer connection that you question as an example; what I am saying is that there is a connection on the timer switch, which is labelled 'HW On'. There are 2 wires going in to it: a black, which originates from the CH power supply switch; and a brown which is going to the boiler.

Exactly.
That means there is power going from the switch direct to the boiler regardless of the timer operation.

If you look at the picture of the wiring for the timer switch, it is the connection one in from the right. You can see the brown wire going down in the cable that goes to the boiler; and there is also a partially hidden black behind it, which goes back to the power supply switch (the power supply switch and the timer sit right next door to each other)
I’m pretty sure of my description of each cable/wire.

Yes, I'm not doubting you but it doesn't make sense.



Here is the normal wiring for two two-port valve system -
Your pump may be wired to the boiler.

 

[Pearlyman]

The power goes from the switch to the timer using the brown wire which is (somewhat bizarrely) conected to the neutral terminal in the timer...

I would have guessed that the timer switch would make the 'HW On' terminal live, when it was programmed to do so (except that never seems to happen !).

I appreciate what you are saying about the wiring not making sense - and I would consider starting again from scratch.
However, it did use to work - wired up as I have described (and as the photos show).
It was even installed by British Gas (about 8 years ago) - so I would have expected it all to have been carried out in a standard fashion...

 

[riveralt]

I appreciate what you are saying about the wiring not making sense - and I would consider starting again from scratch.

Seems like your best option.

However, it did use to work - wired up as I have described (and as the photos show).
It was even installed by British Gas (about 8 years ago) - so I would have expected it all to have been carried out in a standard fashion...

The Photos (2nd & 3rd) seem to show an earth and blue(neutral?) wire connected together in a connector block - that doesn't seem right.

 

[Pearlyman]

I appreciate what you both are saying - but the photos are from before any work was carried out (so as British Gas installed it).

I guess the problem I will have, is if I am able to find a suitable electrician, he will have the same doubts/concerns that you guys have got...

 

[EFLImpudence]

I think you may have described the connections inaccurately.

Ignoring the CPCs (earths) you have only two wires from the switch to the timer but four from the timer to the switch.

The switch is wired up as follows:

N load - Blue (room stat) and blue (timer)
N feed - Blue ring main x 2
L load - Red (room stat) and brown (timer)
L feed - Brown ring main x 2
Earth - Earth ring main x 2, earth (room stat), single earth wire (timer ?)


Timer – Honeywell ST6400C

Has a cable coming in from the central heating power supply switch and a cable going out to the boiler - plus a single yellow wire which goes to the earth terminal.
There are 7 terminals where wires are connected – plus a connection block.

1. Earth - Single yellow wire (CH power supply switch ?)
2. Neutral - Brown (CH power supply switch)
3. Live - Blue (CH power supply switch) and blue (boiler)
4. HW Off - Nothing
5. CH Off - Nothing
6. HW On - Black(CH power supply switch) and brown (boiler)
7. CH On - Black (CH power supply switch)

Connection block linking yellow/green (CH power supply switch) and yellow/green (boiler)

I would swap the L and N at the timer as this is obviously wrong.
Other than that, all I can suggest is you compare the wiring diagram to see if there is anything else wrong.

 

[DetlefSchmitz]

Is it just me or is the y/g wire in the thermostat being used as a live?

 

[EFLImpudence]

R,Y,B surely.

 

[JohnW2]

Is it just me or is the y/g wire in the thermostat being used as a live?

I don't see a Y/G at the stat - all I see are red, yellow and blue insulated conductors, and a bare CPC which disappears to somewhere, but is not connected to the stat's earth terminal. Are we both looking at thge same picture?

Kind Regards, John

 

[DetlefSchmitz]

OK must be the colour rendering on my screen. I saw blue g/y brown. Sorry.