Digital Room Stat

[wsherri]

I would like to replace my ancient room (Bi-Metal Strip) stat with a modern Digital one to give me more accurate temp switch on. The problem I have is that a cannot find a replacement for the wiring configeration I have, here is the wiring on the old Honewell is as follows:
I have three wires 1 Live (Red)
2 Neutral (Blue)
3 Yellow ((Don't Know What This Does)

The Room Stat Has 4 Connections and the wires are connected as follows: 1 = Live
2 = Neutral
3 = Yellow
4 = No Connection

Operation: With Stat Off: Live To Yellow = 250v
Live To 4 = 0v
Neutral To Yellow = 0v
Neutral To Yellow = 0v
Neutral To 4 = 250v

Operation With Stat On: Live To Yellow = 0v
Live To 4 = 0v
Neutral To Yellow = 250v
Neutral To 4 = 0v
Can anyone suggest a Digital Room Stat to replace my old one (Inc Model Number) with possibly no wiring modifications.
I also have an electronic Programmer for automatic switch on of the system

 

[breezer]

the neutral you have is to heat a small resistor to make readings more acurate

the live you have is to feed the controls and the resistor*

Q so how does the boiler know when heat is required?

A the yellow wire (switched live)

so therefor any digital stat will work.

mine for example is battery powered (honest) so in your case you would only need to connect the red and yellow wires.

if your new stat is mains powered then you would need to connect all 3 of your existing wires, live, neutral and swith wire (yellow in your case)

* when i say feed the controls and resistor i mean to supply a live for the resistor, and to supply a permanent live so you can have a switched live for heat demand