Desperate for help.... what's my purple wire for

[MountainAddict]

I'm trying to fit a new thermostat for my underfloor heating. Trouble is, I don't know what colour wire does what. I'm in France and I have a black, blue, purple and red wires aswell as yellow/green i've tried looking in my other thermostats to do a bit of detective work... one of them is connected with 2 blues in the same terminal, which it tells me to do in the instructions... but I don't know what Purple is? as I say i'm in France and it appears to me that they just make it up and hope it doesn't blow up! Can someone please help....

 

[winston1]

I'm trying to fit a new thermostat for my underfloor heating. Trouble is, I don't know what colour wire does what. I'm in France and I have a black, blue, purple and red wires aswell as yellow/green i've tried looking in my other thermostats to do a bit of detective work... one of them is connected with 2 blues in the same terminal, which it tells me to do in the instructions... but I don't know what Purple is? as I say i'm in France and it appears to me that they just make it up and hope it doesn't blow up! Can someone please help....

In France blue is always neutral, green/yellow is always earth. Live, switch wires etc can be any colour except those. But usually red is permanent live. Which leaves your purple and black which I assume are switch wires, one will be live when the thermostat is on and the other when it is off.

 

[MountainAddict]

I'm trying to fit a new thermostat for my underfloor heating. Trouble is, I don't know what colour wire does what. I'm in France and I have a black, blue, purple and red wires aswell as yellow/green i've tried looking in my other thermostats to do a bit of detective work... one of them is connected with 2 blues in the same terminal, which it tells me to do in the instructions... but I don't know what Purple is? as I say i'm in France and it appears to me that they just make it up and hope it doesn't blow up! Can someone please help....

In France blue is always neutral, green/yellow is always earth. Live, switch wires etc can be any colour except those. But usually red is permanent live. Which leaves your purple and black which I assume are switch wires, one will be live when the thermostat is on and the other when it is off.

So maybe I should swap my black wire for my purple wire? is that a bad idea... or a very bad idea??

 

[BLX]

Bit of a late reply, sorry.

If things have been wired in the usual way then.....

Yellow/green = earth
Blue = neutral
Red = permanent live supply

Black = "fil pilote"; this is an optional control/signal wire from a central controller situated in your distribution board to provide overall control of a heating system by talking to your thermostats (it carries mains voltage though!). Your thermostat may have a terminal marked FP.

Purple = could be a live return from a contactor that is sometimes required to handle heating loads higher than the rating of the thermostat. If this was the case then you should also have another wire back to the dist. board as well, but that could be what the black was for (i.e no use of a fil pilote). You need to check what happens to these wires back at the DB before you connect them.

As this is a late reply & you may well have sorted this, do let us know what the outcome was.