Combi and thermostat wiring help

andemz · 14 Jan 2012

Hi all,

I'm just wondering if you could give me some help with understanding the wiring on my combination boiler and thermostat.

I have a supply direct from the CU for the combi, this feeds into a SFCU.
There is a T&E to the thermo stat which is situated downstairs.
The wire from the combi is 4Core and Earth. Blue, Brown, Black and Black with the earth.

Here is a picture of the combo wiring.

Untitled

andemz
14 Jan 2012
1

1) Can anybody help me with what the terminals 3 and 4 are in the combi (The two black wires)

2) What wires for the 4 core and Earth connect to the live and neutral to the thermostat

thanks in advance.

flameport · 14 Jan 2012

Make and model of boiler?
Make and model of thermostat?
Are you fitting a new thermostat, or replacing an old one?

andemz · 14 Jan 2012

I know its a valiant, i will have to check the model number tonight.
The thermostat is a time guard trt033 digital it is a new one

regards

Taylortwocities · 14 Jan 2012

So are you repalcing an existing stat with a new, digital one?

If so, do not change anything at the boiler end. Just connect up the new stat like this: //www.diynot.com/wiki/electrics:how_to_replace_a_room_stat

andemz · 14 Jan 2012

The boiler previously had a programable stat. The wiring has had to be removed and replaced.

The wiring to the stat itself is not the problem it is at the other end at the combi. Within the combi you have the L,N, E and then terminal 3 and Terminal 4, both of which are black wires. When the tennants left, they chopped wires and i have managed the salvage what they cut.

There were two sets of wires going to the thermostat. Each wire was T&E. I presumed this was because it was a programmable one.

The four core was connected to the two thermostat wires as follows:
4 Core blue (4 core) to black (Therm) brown (4 core) to red (therm) and Black (4 core) to red (therm) and Black (4 core) to Black (therm)

Hope this helps

flameport · 14 Jan 2012

That thermostat only requires 2 wires, which correspond to the the black wires at the boiler.

Boiler - Thermostat
3 - L
4 - SL

The other 2 wires (blue/brown) are the power supply for a mains powered thermostat.
However as you have chosen a shonky battery operated thing, they are not required.

RF Lighting · 14 Jan 2012

The brown and blue are the permanant supply to the boiler.

The two black wires are a common and a return for any external controls to the boiler.

diynot

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Combi and thermostat wiring help

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