help identifying wires in my boiler control box

[bhm1712]

hi all im converting to c plan using the honewell sundial centre.

i am just having problems identifying 3 core cables.

going into my existing control box there are 4 cables.

1 is the power in
1 is the cable from the programmer

the other 2 im unsure of. they are small twin and earth cables with 1.5mm2 singles within

i cannot identify what they are. i can rule out the room stat as when i moved in there was no stat, i have since fitted one and the wire goes elsewhere

i can only imagine that one of the cables may be for the immersion heater point in the airing cupboard which is unused, but i cant think why that would be linked into the boiler control box.

any ideas as to what they could be?

 

[bhm1712]

also, they are not the pump or boiler wires as they exit from the bottom of the box

 

[kevindgas]

Why are you converting to a C plan?
surely a S or Y plan would be the logical step just curious really

 

[bhm1712]

cash reasons.

i only need to buy a motorised valve and cylinder stat

to convert to fully pumped is more work involving alot more pipework which i just cant afford

for c plan, all i have to do is add a motorised valve in the heating return and wire in the cylinder stat, the sundial wiring centre is a piece of cake to wire to.

 

[D_Hailsham]

going into my existing control box there are 4 cables.

1 is the power in
1 is the cable from the programmer

the other 2 I'm unsure of. They are small twin and earth cables with 1.5mm2 singles within

A photo of your existing control box might help and/or a list showing what is connected to each terminal - as far as you know - with the unknown ones identified.

i can only imagine that one of the cables may be for the immersion heater point in the airing cupboard which is unused, but i cant think why that would be linked into the boiler control box.

Definitely will not be the immersion heater. That will normally be fed from a separate 15A fuse in your consumer unit/fuseboard . Wiring centres are fed from a 3A fuse.

 

[bhm1712]

i shall do that asap,

its a little difficult to know whats what as whoever installed the system when the house was built just used a fused spurr connection box as the boiler junction box, so inside there is a big wiring mess with a few terminal blocks aswel!

 

[bhm1712]

right,i have had problems uploading pics but i have discovered the following

one of the three cores is the Live, Neutral and Earth to the programmer back plate

the other 3 core is the wire back from the programmer
one core for HW on, and one core for HTG on and the earth is cut off

the other 2 larger wires appear to be BOTH going to the Supply side of the fused switch

so there are 2 lives going to live IN, and 2 neutrals going to Neutral IN and 2 earths, all going to the backplate of the fused connection unit.

why would there be 2 supply wires?

other than that im sorted!

 

[bhm1712]

this is what i have

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[mogget]

Looks like an ordinary gravity hw / pumped ch system to me.

Just a thought, but it's not been supplied from a lighting circuit, has it?

Which breaker / fuse turns it off at the consumer unit?

 

[bhm1712]

i can see what your getting at with the lighting circuit..... so if that is the case one cable will be the supply in, and the other will be the supply back out to the ring

i shall have a look in my fuse board later on and see if your right!

 

[bhm1712]

no,

its fed from the downstairs socket ring main!

 

[mogget]

That's fairly normal - strange with the 1.5mm cores though. Unfortunately I'm not a whizz with electrics, it might be worth posting in the electrics forum if you haven't already.

BTW I do have a friend whose heating is fed by the lighting circuit - weird!

 

[D_Hailsham]

1.5mm cores can carry 16 amp. As the normal fuse for an central heating spur is only 3 amp, I can't see why there needs to be two cables in parallel.

Is the system fed from its own fuse in the spur/plug or is it relying on a fuse in the consumer unit/fuseboard? If there is a plug/fused spur, what fuse does it have? Should be 3 amp.

 

[londonboy]

Can you not follow these cables? I've seen cupboard lights and all sorts spurred off wiring centres and boiler spurs! .. Immersions is the worst one, everyone has a go at spurring off them! Shower pumps, solar controllers.. the list goes on!

 

[bhm1712]

it has its own 3 amp fuse in the fused connection unit, its just originally fed from the 13 amp fuse for downstairs sockets in the consumer unit

i presume the supply is like it is because its part of the ring main so one is the power in, and the other set is the power back out to the ring main

so now all i appear to have to do is pull in a cable from the garage to the airing cupboard for the cylinder stat and i can wire up the sundial plan!

pulling the cable is a task in itself as its from one side of the house to the other!