Sorting out wiring etc for new boiler

[Lobster]

I need to get my gas boiler replaced (pretty urgently as it's died and I'm living off the immersion heater and warm pullovers at the moment! SWMBO unimpressed). Before I get a Man in to do this though, I want (need) to sort out the electrical dog's breakfast left behind by the installer of the original system.

Basically, there's a 4-core-and-earth cable emerging from the ceiling with a single-cored mains cable taped alongside it; these simply dangle down the side of the boiler (Vaillant Ecomax VU226 EH, sited in a corner of the utility room) to underneath it, and then dissappear straight up into a terminal strip. So - no switch or FCU, and four feet of loose mains cable hanging from the ceiling. I now want to sink the mains cables into the wall and terminate them in a switched FCU, from which a short (presumbly 5-core?) flex will emerge and connect to the boiler. This will probably involve lifting the upstairs floorboards immediately above the boiler to install a juction box, as the existing cables are probably too short. But AFAIK there's no such thing as 5-core-and-earth cable is there? What am I missing here?

I think I'm going to have the exisiting boiler replaced with a W-B 30CDI condensing system boiler. For simplicity I was intending it to be controlled by the existing 7-day Sunvic HW/CH programmer upstairs in the airing cupboard which is really the 'nerve centre' of my system, and I will need to add in a roomstat (don't have one currently and so was going to add a wireless one).

Any advice as to the best way forward would be much appreciated. Should I go for a new combined wireless roomstat/programmer - would that remove the need for anything other than standard 2C&E cabling for the new boiler? If not, what? (I should add that it's a long and complicated route for cabling through the house between boiler location and airing cupboard, which I really don't want to have to disturn and fully rewire)

Many thanks David

[Dave Plowman (News)]

System boilers tend to have mains in then a multicore etc to any external controllers. Mine just uses data links so you don't need mains cable. But any decent wholesaler should have a range of mains rated multi-core - TLC do and sell cut lengths. But IIRC, the max they do is 5 core. Still, nothing to stop you using two cables to give the number you need.

[John Rumm]

If you need to joint a cable in situ:

probably too short. But AFAIK there's no such thing as 5-core-and-earth

I think I'm going to have the exisiting boiler replaced with a W-B 30CDI

Prog stats are a massive improvement over normal ones - not only in convenience but also performance IME. You could go the whole hog and use the weather compensating version. It would need to addition of an outside temperature sensor but would add further refinement and fuel savings.

[ARWadsworth]

I cannot see any reason why you should need more than a 4 core flex to a WB

30CDi system boiler

Permanent live Neutral Earth Lr (the call for the boiler to fire)

Adam

[Lobster]

Thanks yes I suppose that would be a possibility. Still confused though - is it the norm to have a 5C&E cable (ie not flex) buried in the wall (Adam W's post about 4C&E duly noted)? How does this normally terminate at the wall, ie where the flex 'emerges'? Trying to envisage an FCU with four or five terminals...

My current programmer allows for HW and CH to go on and off twice a day, all 7 days individually programmable, which seems to fulfil our needs here: other than the roomstat, what am I missing out on, in my ignorance?!

Interesting thought about the weather compensation; hadn't heard of those but TBH our heating bills here are so horrendous that anything I can do to reduce them has to be a good thing.

I note that W-B do a weather compensation gizmo for the boiler I'm interested in:

However as I understand it this FW100 is a combined wired roomstat, programmer and weather compensator, which would mean I'd need to run cables from the preferred roomstat site to the boiler, and also the preferred exterior wall which would make it a no-no on those counts if I'm right? Confusingly (to me) it can also be fitted within the boiler, so how can it serve as a roomstat then? Or doesn't it?

Thanks David

[Lobster]

[victormeldrew mode]

I don't belieeeeeve it!

[/victormeldrew mode]

The immersion heater element (approx 7 years old and barely ever used) has just packed up. And this is an unvented HW cylinder so no quick diy repair.

So I may as well just bend over, put my head between my legs and kiss my arse goodbye...

David

[John Rumm]

One should use conventional solid core cables (i.e. T&E or 3&E or any other bigger versions you can find for the fixed wiring, and then use a flex outlet etc for the flex jump to the boiler. The reality is that people often wire these things all in multicore flex.

The ability to have the heating set to maintain different temperatures throughout the day, and also to enforce a minimum you don't want it to drop below.

Some of the proprietary modern prog stats will also cope with switching flow temperatures on the boiler, so that you can run your heating at a more efficient lower flow temp, and yet still have the hot water reheated to a decent temperature.

Basically they attempt to drive heating at its most efficient flow temperature, but taking into account the actual outside temperature and the typical heat loss profile of the building. The result should be better comfort an lower overall costs since the boiler is run at maximum condensing efficiency all the times it can be, but you don't get the family jewels frozen off on the days where it is -5 outside.

Yup, I was looking at that the other night (I am currently going through the same exercise finding suitable replacement boiler etc)

It probably does not act as a stat in that case, just a weather compensator. I don't know about that particular one, but some allow an additional remote temperature sensor to be connected to act as the stat.

[John Rumm]

With the posh controls you need a pair of wires for the "bus", plus the traditional three for the power supply. You may also need another couple for the bus connection to the external sensor, but they don't always have to be connected at the boiler.

(oh, should have mentioned in answer to Lobster's other point about wiring - you can get wireless versions of much of this kit from most makers. That may simplify the wire routing issues)

[John Rumm]

See if you can tell SWMBO to do that, since you have a great idea for keeping her warm ;-)

[Andrew Gabriel]

Flex is permitted for fixed building wiring. It's not normally used because it's more expensive and doesn't clip into straight lines, but if you need many more cores than are available in normal solid core, then you can use multicore. Factors such as circuit protection appropriate to the earth fault loop impedance still apply, so don't use long lengths of

0.75mm multicore even though voltage drop isn't a problem.

I have 7-core linking my Keston boiler back to the (equivalent of) the wiring centre (actually home automation heating interface), but I use its extra signalling outputs (burner on, boiler locked-out).

[Andrew Gabriel]

Worth checking it isn't just a poorly made connection which burned out on first use.

(I just checked an immersion heater and found exactly this, whilst contenplating a drain down to replace the feed pipe from the expansion tank, which I suspect has furred up.)

;-)

[js.b1]

Flex is permitted for fixed wiring as long as... a) terminals designed for it.

- Open any SFCU, note the cord outlet

- Note terminals for flex side same as "fixed" side b) bootlace ferrules used.

- Bootlace ferrue ratchet crimp not like RYB crimp

- Note the above, saves =A312-20 for tool

Cable exiting wall... a) 1G backbox with Abox (mounting holes align) b) BESA box sunk with BESA box on top & gland c) BESA box sunk with masterseal jn-box (4-way term & glands) d) 1G backbox with 1-2-3-4 MK Grid cord outlet fittings

If you need to join cable... a) use the masterseal as above (bit pricey) b) Wago Lever clips which are fast and ideal

Ebay & Farnell list the Wago lever clips, very useful & fast.

[John Rumm]

Anyone tried their pushwire connections:

look like a niece alternative to chock blocks....

[Jules]

Can you run it all 'externally' via some metal cable armour (I can never remember what the technical name for the stuff is!)? As it's going to have a sodding great boiler next to it, it doesn't seem to matter to me if the cable run looked a bit 'industrial', and it'd be a lot quicker to do than burying in the wall (and easy to screw around with later if you wanted)

[John Rumm]

SWA = Steel Wire Armoured perhaps?

have a sodding great boiler next to it, it doesn't seem to matter to me if

There might be a slight terminology gape here; the "sodding great boiler" being discussed here is a small neat gas fired central heating boiler[1], not a huge great hot water cylinder with immersion heater, which IIUC is what is often termed a "boiler" in the US.

The electrical demands are very small as well - a 3A supply for the boiler to run its electronics and pump and fan, and some control wiring to hook up the stats / programmers etc.

[Lobster]

Oh it just gets better and better.

The heating engineer has told me the cylinder (and immersion heater) are now obsolete and he's having real trouble sourcing a new heater. Only one he can find cost well into three figures!

Anyone got any useful links for plumbing spares I could try? I've looked everywhere I know, and googled to no avail. The element is an

11", 3kW Redring LU 11 TC

Thanks David

[Andy Cap]

There's an 11" element on Ebay. Don't know if it's suitable.

Andy C

[Owain]

A google suggests that LU11TC is used in some Gledhill cylinders so either they or Redring might be worth approaching

[ericp]

Have you tried Vaillant? They should have some for a not very old piece of equipment.

[geoff]

Could ask here