Possible faulty CH timer

[Pearlyman]

I raised this problem on the Electrics UK forum a couple of days ago and the guys over there were extremely helpful in enabling me to get a much better understanding of the issue.

However it now seems to have run its course on that forum so I am hoping that someone on here may be able to help me take it to completion !

In summary, I carried out some building work a few weeks ago, part of which involved me taking down and rebuilding a stud partition wall where the power supply and timer switch for my central heating system where located.

I was very careful in that I took photos and made notes about the wiring so that I could put them back exactly as they were.

I was pretty sure I’d done that – but when I switched the power back on, whilst the timer came on – the green LED on my Baxi 100 HE didn’t.

I called out British Gas in case it was boiler problem – but the engineer managed to blow the fuse in the power supply when he manually moved one of the valves.
He then told me I had an electrical problem – and left !

I’ve checked, double checked – and triple checked all of the wiring.
I’ve also followed back the wires to my main wiring centre (I have an ‘S’ plan set-up) and pretty much everything appears as I would expect.

The only exception to this comment, is the blue wire in the timer cable, which for some reason, appears to change to an earth (G/Y) before it is sent on to the boiler ! (the boiler only has a switch live - no permanent live).
However, this has always been the case – and I have photographic evidence to prove it !

Whilst I originally thought that I must have wired up something incorrectly, I am now wondering if the problems (lack of power to the boiler and the power supply fusing) could be caused by a fault in the timer ? (it is an old Honeywell ST6400C)

I am trying to contact an electrician to take a look – but I am struggling to get a reply…

All help/comments gratefully received

 

[Pearlyman]

Is anyone able to advise on whether the problems I have encountered (no power light on the boiler and the power supply switch fusing) could be caused by a fault in the timer ? - or do I need to wait until I can get hold of an electrician to check things out…?

If anyone is also able to explain why the blue wire in the cable from the main wiring box (where I think it is connected to 2 x oranges to the valves and a brown to the pump) to the timer, effectively becomes an earth for the boiler as it passes through the timer, then that would be appreciated as well !
In truth, I suspect this is impossible to explain ! – but would it account for the problems I am witnessing (even though I’m pretty sure this is how it has always been set up…)

Thanks.

 

[GuessMan]

The oranges are switched live from the zone valves and should never be connected to earth regardless of the colour of the wiring. Download the Honeywell wiring diagrams and completely rewire ! Check the manufacturers instructions to see if the boiler needs a permanent and switch live also.

 

[Pearlyman]

Thanks for the reply.

The connection of the blue is baffling me as well - but I'm pretty sure that is how it is has always been (I have photo to prove it !)...
What should the blue (that is connected to the oranges in the wiring box) be connected to, in the timer ?

I checked the manufacturers instructions and the boiler only requires a switch live (no permanent live)

 

[GuessMan]

Would need to be there to know. Asi said download the Honeywell wiring guides - they are free and very clear.

 

[Pearlyman]

I’ve got access to the wiring guide – but the fact there is no permanent live on the boiler makes is making it difficult for me to relate to my set-up…

The timer is currently connected to the L,N,E in the power switch (the L and N seem to be the wrong way round – but I believe they are interchangeable).

The CH On connection goes to the room stat in the wiring box.

The HW On connection goes to the cyclinder stat in the wiring box – and also provides the switch live for the boiler…

As per above, the boiler gets its switch live from the timer (via HW on) and it’s neutral from the timer.
Then there is this earth connection, which is bizarrely joined up with the switch lives for the vales and the live for the pump, in the wiring box !

I appreciate that can’t be right – but where should the switch lives from the valves and the live from the pump possibly go to ? (accepting that it's impossible to say categorically without seeing it)

 

[EFLImpudence]

Moonlighting eh?

I’ve got access to the wiring guide – but the fact there is no permanent live on the boiler makes is making it difficult for me to relate to my set-up…

S plan only uses switched lives.
It is down to the type of boiler whether a permanent live is used.

The timer is currently connected to the L,N,E in the power switch (the L and N seem to be the wrong way round – but I believe they are interchangeable).

Only insofar as it is alternating current.
A fault would make the appliance live rather than blowing the fuse.

The CH On connection goes to the room stat in the wiring box.

Correct.

The HW On connection goes to the cyclinder stat in the wiring box – and also provides the switch live for the boiler…

Correct, as does the room stat.

As per above, the boiler gets its switch live from the timer (via HW on) and it’s neutral from the timer.

SL via HWon, Tank stat, HW valve and/or
SL via CHon, room stat, CH valve
although the actual feed is from a permanent live in the valves.

Then there is this earth connection, which is bizarrely joined up with the switch lives for the vales and the live for the pump, in the wiring box !

Likely naughty plumbers using earth as live.

I appreciate that can’t be right – but where should the switch lives from the valves and the live from the pump possibly go to ? (accepting that it's impossible to say categorically without seeing it)

See Electric forum. Hang on just meant wait. I have answered.

 

[twgas]

, it sounds like you've done it wrong.
Had a look at pics, can't really tell what is what in the junction box, and are there before and after pics?

 

[Pearlyman]

, it sounds like you've done it wrong.
Had a look at pics, can't really tell what is what in the junction box, and are there before and after pics?

Hi Mick,

All of the photos (apart from the one I posted today) are from before the work was carried out. What I was trying to do, was get things back into the same state (which I naively thought, meant they would work !).

ELF has kindly provided me with an ‘S’ plan wiring diagram, which I completely understand – and can replicate my set-up…

The only issue, is the changes that I am having to make from what was there previously (as is shown in the photos).

The main issue concerns the blue and Y/G that are shown connected in the pattress for the power supply. I’m pretty sure that that the blue comes from junction 10 in the wiring box (the only other possibility is the neutral for the power supply itself – but that makes even less sense). However it is connect to a Y/G, that then passes through to the timer, where it is connected to the Y/G (ie. earth) for the boiler !

This is how things were set-up – and how they worked is beyond me (and EFL !).

All I could think was that the Y/G that goes to the boiler, becomes the live inside the boiler – but I took the cover off the boiler and it remains Y/G inside.

Consequently, that connection has me completely baffled…

I’ve now taken the blue from junction 10 in the wiring box and connected instead, to the live in the boiler. That is obviously a lot more logical – but it is a big change to make !

I’ve also connected the Y/G that is going to the boiler, to earth. Again, this seems completely logical – but is the opposite of what I photographed as being there previously….

At the end of the day, I simply can’t explain the photos. I know I took them before the work started – and I know the boiler was working then.

However, it would appear that all I can do now, is ignore them and wire it correctly from scratch (which is what EFL is helping me to do)…

I’m just not looking forward to that moment when I switch the power back on

 

[Pearlyman]

Moonlighting eh?

I must admit, I didn't expect to see you over here

Is solving the electrical problems of the UK not enough of a challenge ? - or are you looking to move into plumbing because that's where the money is