A real baisc noob question for you chaps. why have THREE wires at a standard thermostat, ie a LIVE,ON and OFF wire, why not have a simple live and switch wire setup. Im asking this as i recently changed my basic mechanical stat for a digital and the 12 & 3 cable markings were not the same as the old stat. ie the C/H will not come ON until the SET ambient temp is reached, rather than turning OFF, obviousley i had the switch wires crossed.
lamens C/H thermostat question
- Thread starter efiste2
- Start date
The thermostat can also be used for cooling, so when the temperature is above that set, the cooler will come on to bring the temperature down. Manufacturers, unfortunately, have different names for the same terminals, or just numbers. So DIYers get confused by: Call, Sat, NO, NC, 1, 2 etc.
Older stats often needed three wires: Live, Neutral and Switched Live. Modern digital stats do not need the Neutral.
thanks for helping, below is the diagram from the instructions. am i correct in thinking terminal 3 or C should be the LIVE and terminal 2 should be the call for heat of ON switch wire. and terminal 1 really need not be connected 
If the wire marked BL is Blue, it is probably the Neutral; you can check this at the other end. If it is connected to several other blues and to the Blue from the main power switch it will be the Neutral. In which case it is not required and should be disconnected at both ends and made safe (insulation tape, cut the bare ends off etc)
The red wire is probably the live from the timer CH ON and should got to the C terminal.
The Yellow wire will be the switched live and should be connected to the ON terminal.
Thanks for the expert advice, But i think i have been sent a red herring from the stat or it is not compatible with my timer. The C/H timer seems to have gone faulty. Ie it turns on but will not turn off, even thought the display and the led go out the C/H remains on and the live at the stat remains live. Is this the case that its not a good idea to mix n match timers and stats My timer is a Honeywell ST6400C Programmer and the original mechanical stat came with it as part of a kit, But i fitted a SUNVIC digital thermostat. last month, and all has been ok until today when i came in from work and the S/F 3A fuse supplying the heating system had blown.
My timer is a Honeywell ST6400C Programmer and the original mechanical stat came with it as part of a kit, But i fitted a SUNVIC digital thermostat. last month, and all has been ok until today when i came in from work and the S/F 3A fuse supplying the heating system had blown.Sounds as if the Yellow is the Live and Red the switched live, so when you connected the Blue (neutral) to 2 and turned the stat up you would have shorted the yellow (live) and blue (neutral). Result - blown fuse.
Mix and Match is no problem - provided you know what you are doing. It goes on all the time!"
Mix and Match is no problem - provided you know what you are doing. It goes on all the time!"
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