Smart thermostat wires

[derekmay]

Trying to install a smart thermostat,
I have 4 wires red, yellow, blue and earth,
And this smart meter wiring diagram baffles me.
1st photo old thermostat,

 

[brianmoooore]

À = 4
N = 3
C = 2

Printing on the back of the new 'stat indicates a second, volt free, switch connected to 5 and 6, but the paperwork shows a NTC resistor = temperature sensor connected to those terminals.
Your diagram for the old 'stat show B as neutral. This is not correct. B is the live end of the backset resistor.
If this is being fitted into a flush metal box, then the earth should be connected to that.

 

[derekmay]

À = 4
N = 3
C = 2

Printing on the back of the new 'stat indicates a second, volt free, switch connected to 5 and 6, but the paperwork shows a NTC resistor = temperature sensor connected to those terminals.
Your diagram for the old 'stat show B as neutral. This is not correct. B is the live end of the backset resistor.
If this is being fitted into a flush metal box, then the earth should be connected to that.

So 2 is blue 3 is red, and 4 is the yellow wire

 

[brianmoooore]

Can't answer that. I've no way of knowing what colour was attached where on the old 'stat. Pics before you disconnect are always good.

 

[derekmay]

Can't answer that. I've no way of knowing what colour what attached where on the old 'stat. Pics before you disconnect are always good.

On the photo, a is yellow, b is brown, only 2 wires was connected.

 

[brianmoooore]

Brown??? no mention of a brown wire in the OP.

 

[derekmay]

Brown??? no mention of a brown wire in the OP.

Sorry red

 

[brianmoooore]

On the photo, a is yellow, b is brown (red), only 2 wires was connected.

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This is an unusual way for a thermostat to be connected. It's connected to break the circuit as the temperature rises - most are connected to close the circuit with temperature rise.
Also, conventionally red would be connected to A and yellow to B, although with just two wires connected it wouldn't make any difference to the operation of the circuit.
What is this 'stat connected to. You may have to examine the source end of the wire to see what's what. The blue may be neutral, but may not be connected at all.

 

[derekmay]

---

This is an unusual way for a thermostat to be connected. It's connected to break the circuit as the temperature rises - most are connected to close the circuit with temperature rise.
Also, conventionally red would be connected to A and yellow to B, although with just two wires connected it wouldn't make any difference to the operation of the circuit.
What is this 'stat connected to. You may have to examine the source end of the wire to see what's what. The blue may be neutral, but may not be connected at all.

A Worcester green Star 4700 combi boiler

 

[brianmoooore]

Any external programmer and/or wiring centre? Worcester 4700 manual doesn't show connections to a 'stat.
Red, yellow and blue wire indicates that the wiring is much older than the boiler.