I would like to upgrade my central heating from gravity hot water to
fully pumped. I have bought a cylinder thermostat and it says to
connect it with 2 core flex.

Do I run a long length of flex all the way from the cylinder upstairs
to the boiler, pump, and valves, downstairs or should I run a short
length of flex from the cylinder thermostat to a junction box in the
airing cupboard and then use twin and earth for the long run to the
boiler? Or doesn't it really matter? Do you use whatever is to hand?

On the subject of using whatever is to hand, I am also replacing the
old clockwork time switch with a digital programmer. I know I can buy
multicore wire to connect to this but if I have 2 or 3 core cable
already, can I just use a few lengths of these?

I have something in the garage. I cant remember if it is 2 or 3 core.
If it is 3 core, can I use this for the thermostat and just snip off
the earth or is that considered bad practice? Should earths always be
connected to something?

If it is 2 core, is it alright to use that to run from the wiring
centre to the programmer since the programmer does not need an earth?
Or is it good practice to always have an earth (there is a brass
terminal in the back plate to connect one to if required).

In article ,
Robert wrote:
I would like to upgrade my central heating from gravity hot water to
fully pumped. I have bought a cylinder thermostat and it says to
connect it with 2 core flex.

Do I run a long length of flex all the way from the cylinder upstairs
to the boiler, pump, and valves, downstairs or should I run a short
length of flex from the cylinder thermostat to a junction box in the
airing cupboard and then use twin and earth for the long run to the
boiler? Or doesn't it really matter? Do you use whatever is to hand?

Flex all the way would be fine. Some would use TW&E as it's cheaper if
they already have some. I generally use high temperature flex to a
cylinder stat - butyl or similar - which is more expensive than ordinary
flex so perhaps another reason to use TW&E if it's a long run. And use a
flex outlet box to secure the flex at the 'wall' end so is a convenient
place to change to a different cable.

On the subject of using whatever is to hand, I am also replacing the
old clockwork time switch with a digital programmer. I know I can buy
multicore wire to connect to this but if I have 2 or 3 core cable
already, can I just use a few lengths of these?

Yes - but the earth wire *must* only be an earth. Colour code the others
at both ends to aid identification. But for the cost of a few feet of
multicore...

I have something in the garage. I cant remember if it is 2 or 3 core.
If it is 3 core, can I use this for the thermostat and just snip off
the earth or is that considered bad practice? Should earths always be
connected to something?

If there is no earth connection at the stat, don't snip off the earth but
tape it back to the sleeve. Might be needed one day. Connect it at the
other end.

If it is 2 core, is it alright to use that to run from the wiring
centre to the programmer since the programmer does not need an earth?
Or is it good practice to always have an earth (there is a brass
terminal in the back plate to connect one to if required).

Providing an earth even if not needed future proofs things in case it is
later.

--
*Sherlock Holmes never said "Elementary, my dear Watson" *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 07 Feb 2010 10:19:14 +0000, Robert wrote:

I would like to upgrade my central heating from gravity hot water to
fully pumped. I have bought a cylinder thermostat and it says to
connect it with 2 core flex.

Most cylinder stats are single pole change over (indeed some wiring
"plans" require it to be so) and earth. As pulling cables in is the
hard part I'd use 3 core and earth to a cable outlet near the
cylinder and then heat resistant 3 core and earth to the stat.

The back plate of most (all?) programmers doesn't really have enough
terminals or space for connecting up all the required cables neatly
and sensibly. Use a proper wiring centre, something like the Danfoss
WC4B, this has enough terminals to terminate all the wires form all
the cables and then have short "jumpers" between terminals to connect
up the system as required.

To be honest the questions you are asking are rather basic and I
wonder if you would be better off getting an electrician (with
experience in heating controls) to do the work.

--
Cheers
Dave.

On Sun, 07 Feb 2010 11:20:26 +0000 (GMT), "Dave Plowman (News)"
wrote:

Flex all the way would be fine.

Thanks. I wasn't sure whether the convention was to use twin and earth
for the fixed part but I think there is an advantage to using flex all
the way because as you say, at the other end it will have to go into a
wiring centre and won't that involve some loops and curls which twin
and earth does not like?

Also the pump, boiler, and valves all have flex so is it better to
have all flex connections in the wiring centre or can you mix and
match flex and solid twin and earth?

Yes - but the earth wire *must* only be an earth.

Yes, I knew that, sorry I should have said.

But for the cost of a few feet of multicore...

True but I was thinking of doing it on Sunday when the shops are
closed and I have some 2 core at home.

Providing an earth even if not needed future proofs things in case it is
later.

If I used a multicore cable I would be happy to have an earth for
future proofing. I was thinking of using three lengths of 3 core
cable: using the earth wire as an earth and taping the blue wires with
a brown flag or sleeve. Only that way I would have three earth wires
at the programmer and three wires at the other end in the wiring
centre. It seemed a bit redundant having three earths going the same
place and I am sure the wiring centre will be full enough; that's why
I was wondering if I could omit the earths. As it happens it is 2 core
cable I have bought (ready for the stat). Could I use this if
necessary? I will probably wait until Monday and get the multicore now
but it would be nice to know for reference!

On Sun, 07 Feb 2010 11:43:09 +0000 (GMT), "Dave Liquorice"
wrote:


Most cylinder stats are single pole change over (indeed some wiring
"plans" require it to be so)

They do

and earth.

The Honeywell L641A is double insulated and has no provision for an
earth

http://www.screwfix.com/prods/40051/...-Cylinder-Stat


Is double insulation something unique to Honeywell stats?


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