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Topic Title: Boiler Wiring
Topic Summary: Why must you have a pump neutral?
Created On: 25 September 2012 08:14 PM
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 25 September 2012 08:14 PM
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Grumpy

Posts: 460
Joined: 09 January 2009

Wiring a boiler swap today. I suppose I got my hopes up, in and out in a couple of hours, as I knew the original boiler had a pump over-run which is the usual cause of time consuming additional wiring. But no, the old boiler was only wired for pump live but the Worcester boiler wanted pump live and neutral. I have come across this before on a Valiant but as that was first fix it presented no problems. Today, however, was a horror story. I rang Worcester to ask if I could omit the pump neutral but was told no and if I do I will invalidate the warranty. When I asked why he said he didn't know why but if I do . . .
So, given that the whole of the heating circuit is controlled by one FCU and, hence, one neutral can anyone explain why the pump neutral has to come from the boiler rather than the wiring centre?
(I don't want to go on but it took all day, all chuffin' day, involving two lofts, various wardrobes and an airing cupboard each absolutely rammed with junk. No I'm not cleansed yet)
Thanks for any replies, beer I think.
 25 September 2012 08:27 PM
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alanblaby

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I do a lot of boilers, mainly Glowworm, and they always have their neutral connected together somewhere, so it means one less core needed to get from the boiler to the wiring centre/junction box.
If you look at the wiring diagram of the system you are installing, there is probably a joined neutral in it.
Glowworm need 8 core cable, I usually put in 2 x 5 core, as I cannot get 8 core locally - Perm.L, switched L, pump L, neutral, earth, CH on, CH off, HW on.

Check the diagram first, but I suspect you will only need the one neutral feed.
 25 September 2012 08:36 PM
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peteTLM

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if you look in the internal wiring, they are normally linked to the other N terminal internally, so the pump neutral, as long as its on the same circuit, same spur etc i dont see a problem.
Unfortunatly in these times, boiler 'engineers' are easily upset, so keep it simple for them.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 25 September 2012 08:40 PM
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Grumpy

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Alan, I can assure you that I checked the diagram most thoroughly and followed that with a tearful phonecall to Worcester technical.
This is a regular boiler with the pump remote. Worcester require permanent live and neutral, switched live, and pump live and neutral (plus cpc's). As you say "the neutrals are connected together somewhere" and they all come from one FCU so no issues with back feeding (as Valiant have it) so why must the pump neutral eminate from the boiler?
 25 September 2012 08:43 PM
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peteTLM

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As well as that, they are often fused internally live AND neutral, work that one out for compliance if the neutral fuse goes first.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 25 September 2012 08:50 PM
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Grumpy

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Well, I'll keep you informed. If those buggers at Worcester think they can put me through days like today without good reason then . . .
Then I shall ask them politely tomorrow!
 25 September 2012 09:00 PM
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SKElectrical

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Originally posted by: Grumpy
So, given that the whole of the heating circuit is controlled by one FCU and, hence, one neutral can anyone explain why the pump neutral has to come from the boiler rather than the wiring centre?

I dont see why an external pump cant have a neutral from elsewhere on that circuit.
Anyway surely the pump was next to the boiler?
 25 September 2012 10:29 PM
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Martynduerden

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Worcester normally require the pump to be fully supplied and hence isolated from the boiler, in fact they require as part of the Manufactures instructions that all external controls are supplied from the boiler.

FCU>Boiler>External Controls>Boiler.

Most modern boilers have pump overrun to prevent overheating, external pump connection whilst not always an issue prevent the boiler from knowing its status.

-------------------------
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Martyn.

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www.electrical contractors uk.com
 25 September 2012 10:33 PM
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Grumpy

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The pump is in the airing cupboard, with the wiring centre, on the opposite side of the house. If it was chuffin' next to the chuffin boiler there wouldn't be an issue, would there? No SK, I don't see why either but according to Worcester it would invalidate their poxy warranty. The question, yet to be answered, is why.
 25 September 2012 11:17 PM
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Martynduerden

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Ask the plumber to move the pump not a big job dependent on layout.

-------------------------
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Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 25 September 2012 11:19 PM
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Martynduerden

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Originally posted by: Grumpy

The question, yet to be answered, is why.


See above / below depending on your layout


Most modern boilers have pump overrun to prevent overheating, external pump connection whilst not always an issue prevent the boiler from knowing its status.


-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 26 September 2012 07:09 AM
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primo

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Originally posted by: Martynduerden

....in fact they require as part of the Manufactures instructions that all external controls are supplied from the boiler.



FCU>Boiler>External Controls>Boiler.





I wired a Vaillant in this way and the plumber told the builder it had been wired up wrong!

Although I did ask Vaillant at the time exactly why it had to be wired like this and they never really answered the question.

Makes sense though as why would you need power to the controls if the boiler is not on?
 26 September 2012 08:06 AM
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alanblaby

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The boiler is always 'on'. It is, usually, controlled by the programmer, the position of the valves and the thermostats. If wired, they need L/N/E on permanently.

These turn on the switched live to the boiler, which will then fire up. Once the room/cylinder has reached the set temperature, the stats will turn off the boiler, or close/open one of the valves, which will switch the boiler.
So the 'system' needs a live/neutral/earth at all times to work properly.

Of course, older boilers with no external controls can be just turned on and off whenever required.
 26 September 2012 09:42 AM
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daveparry1

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The question, yet to be answered, is why
----------------------------
Must admit I haven't followed this thread fully Grumpy but are they saying that without a dedicated neutral for the pump the over-run couldn't work, thus causing possible overheat of the heat exchanger therefore invalidating the warranty?
Sorry if i'm off the track but as i said I havent fully followed the post!

Dave.
 27 September 2012 09:46 PM
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Martynduerden

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Originally posted by: daveparry1

The question, yet to be answered, is why

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Must admit I haven't followed this thread fully Grumpy but are they saying that without a dedicated neutral for the pump the over-run couldn't work, thus causing possible overheat of the heat exchanger therefore invalidating the warranty?

Sorry if i'm off the track but as i said I havent fully followed the post!



Dave.


Correct

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 27 September 2012 09:49 PM
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stateit

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Originally posted by: Martynduerden


Correct


Well, I've drawn it out and still can't see why the N can't be commoned anywhere along the circuit.

Mind you, I did only get a 'C' at Art.

-------------------------
S George
http://www.sg-electrical.com
 27 September 2012 09:54 PM
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Martynduerden

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Originally posted by: stateit

Originally posted by: Martynduerden


Correct


Well, I've drawn it out and still can't see why the N can't be commoned anywhere along the circuit.

Mind you, I did only get a 'C' at Art.


It is more to do with the boiler electronics and its ability to sense the pump functioning electrically and for the diagnostic functions.

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 28 September 2012 08:09 PM
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weirdbeard

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Must admit that I've wired a fair few boilers where they have a separate LNE output for the pump, not had any issues so far when for neatness of wiring I have used a single 5 core flex to the boiler, ie permantent live/n/e/switched live in/pump output live - the instructions do say if in doubt consult an electrician! (which I am, so i say it's ok)
 29 September 2012 12:45 PM
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sparkingchip

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Worcester want all the external controls wired through the boiler so when the boiler is turned off all the associated equipment is dead and safe as well, so the boiler is a main isolator electrical supply as well as the SFCU rather than it just being the SFCU.

No reason you cannot wire connections outside the boiler other than Worcester don't like it!

Andy
 02 October 2012 07:29 PM
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OldSparky

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well if you want my two peneth,, wire as you see fit..

pick up the neutral else where on the same circuit, test it so the pump will over run.. cant see any reason why not..

also tell the plumber to fit a boiler without over run..

on another note i normally fit a 3 pole fan isolator next to the boiler for isolation if the spur is else where. a customer rang me to say she had the boiler commissioned and the engineer told her it was dangerous because the switch next to the boiler was not the correct one.. so this is telling you what gas fitters know about electrics..
IET » Wiring and the regulations » Boiler Wiring

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