wiring a digital room thermostat.

[madsey]

Hi guys,
I'm replacing my old room thermostat with a digital one and i'm not to sure about wiring it up.
I've removed the old one and i now have 4 wires sticking from the wall,
RED
BLUE
YELLOW
and EARTH.
They are all dead until the heating comes on and then the RED wire is live.

The new thermostat only as 3 terminals marked,

NO
COM
NC

Can anybody please tell me how to wire it up,i'm totally stumped.

Thanks for all replies,madsey

 

[pdcelec]

What do the instructions that came with it say on them?

 

[madsey]

The instructions says,

live to COM terminal and return from boiler to NO terminal but no
mention what to do with the other wires!!!!

Anybody got any ideas ????

Thanks,madsey.

 

[pdcelec]

This is not a definitive answer but my guess would be

RED to COM
YELLOW to NO
EARTH to the earthing point or backbox
BLUE - unused (probably a neutral that may have been required with the old stat)

This would need confirmation with a multimeter but is an educated guess based on experience (since the red is live when the boiler comes on I would suggest that this certainly goes to COM)

 

[plugwash]

at a guess blue is a neutral not needed with your thermostat (so cap it off with terminal block) and then connect the two remaining wires to the com and L1 terminals of your thermostat (doesn't matter which way round).