Wire out of back of thermostat control

[nerf]

Hi can anyone tell me which wires go to which connection on a siemens landis&staefa raa02 room thermostat please there are 4 wires going to it blue, black, brown and earth there are 3 connections in control unit the brown is to the 1st 1 , the second 1 has nothing going to it and the 3rd one has the blue wire connected, the black wire has come out when decorating , tried to put it to the second connection and it just blew the fuses in the boiler,does anyone know where it goes and thanks in advance for any replies they are much appreciated

 

[croydoncorgi]

see http://www.eci.siemens.com/misc/dow...a/English/file/binary/raa02_1000000066114.pdf

This roomstat seems to be a 3-wire type: Live, Switched Live and Earth. If there's a 4th wire it MIGHT be left over from a 4-wire roomstat which requires a Neutral connection as well. If so, it needs to be carefully insulated and put out of the way behind the roomstat housing.

TURN OFF THE ELECTRICITY BEFORE YOU TOUCH ANYTHING

 

[nerf]

Thanks for that croydoncorgi, the thermostat is a recent addition to the central heating as we have had to have a new boiler fitted a few months ago, up until then there was no thermostat control on the wall so the wires aren't from a previous installation I thought it was spare also but it seems like the central heating doesn't come on by itself now were as before it did hope this helps a little more, I can take a picture of it to show you but don't know if I can put it into this forrum or how to put it in here.Thanks in advance once again.[/img]

 

[gas4you]

Normally blue would be neutral, but link CC has given states no neutral needed.

Brown would normally be live in, black =switched live and blue neutral.

If heating is not working then I would suspect that black is switched live.

Cant see why you have a neutral though

 

[Lincsbodger]

hi. sorry to revive an old thead, but ive got the same problem.

Replacing the old mechanical central heating programmer with a brand spanky new one, the room stat has four wires to it, live feed, switched live return, earth, and theres a incoming neutral wire. Its very very old, is this programmer and stat.

Ive partially taken the stat apart, i cant see why it needs a neutral. Theres nothing in a stat that needs continuous power, like a clock motor. The onlything on the circuit board in side is a small silver tub that goes to the incoming live - could t be some sort of spike suppressor to cut down the radio interference - which might be why its got a neutral, since mechanical contacts opening and closing certainly do make RF interference? Thats the only thing i can see on the neutral line.

 

[twgas]

It might help if you said what model of 'stat you are replacing with what!
Also it's better to start a new thread.

 

[TicklyT]

Some 'stats incorporated an 'anticipator' to make them more sensitive - basically it's a very small electric heater, needing live and neutral connections to make it work.