I'm replacing my room therrmostat with a programmable one, but the
wiring doesn't seem to correspond. Below is an (Arthur) ASCII sketch
of the existing wiring, with the colours alongside.
_____ _____
-|_____|-|_____|--¬
| |_ 3 N (Blue)
|_______________
\|____ 2 H (Yellow)

In article ,
Hugo Nebula abuse@localhost wrote:
_____ _____
-|_____|-|_____|--¬
| |_ 3 N (Blue)
|_______________
\|____ 2 H (Yellow)
.
|______ 1 TL (Red)

The new thermostat has connections for Common, Heating Satisfied and
Call For Heat. Which is which? Am I right in thinking H (yellow) is
Call for heat, TL (red) is Common, leaving N (Blue) as Heating
Satisfied?

If it's any help, I've traced the wiring back to the main wiring
block, and the red of the existing thermostat connects to the live
from the programmer, the yellow connects to the white of the 3-way
valve, and the blue to blue wires from the pump, 3-way valve and
boiler.

The blue is likely neutral and not needed on a battery operated stat.
Insulate and tape up out of the way. (It was needed for a heating coil in
the old stat to improve the accuracy and response of a bi-metallic strip;
modern units use a solid state sensor which is vastly more accurate and
reacts near instantly.)

To simply replace the existing one, red to com and yellow to call for
heat. The heating satisified - the normally closed contact - would be for
'special use'. To use it would likely need a total re-jig of your wiring
and IMHO isn't needed to replace a 'standard' thermostat.

--
*The colder the X-ray table, the more of your body is required on it *

Dave Plowman London SW
To e-mail, change noise into sound.

In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:

I'm replacing my room therrmostat with a programmable one, but the
wiring doesn't seem to correspond. Below is an (Arthur) ASCII sketch
of the existing wiring, with the colours alongside.
_____ _____
-|_____|-|_____|--¬
|_ 3 N (Blue)
_______________
\|____ 2 H (Yellow)
.
|______ 1 TL (Red)

The new thermostat has connections for Common, Heating Satisfied and
Call For Heat. Which is which? Am I right in thinking H (yellow) is
Call for heat, TL (red) is Common, leaving N (Blue) as Heating
Satisfied?

If it's any help, I've traced the wiring back to the main wiring
block, and the red of the existing thermostat connects to the live
from the programmer, the yellow connects to the white of the 3-way
valve, and the blue to blue wires from the pump, 3-way valve and
boiler.

You haven't been listening, have you? g [This is a fairly frequent
question in this NG!]

Your old stat had a little heater in it to warm up the innards when the
heating was on, and to make it more responsive - reducing overshoot etc. The
blue (neutral) wire is the return for this heater.

Your new electronic stat doesn't have/need an internal heater, and only uses
2 wires. The blue wire *must not* be connected - but must be insulated and
made safe.

The other 2 wires connect to COM and Call for heat - it doesn't really
matter which is which since it's just a switch, but convention has it to
connect Live (R) to COM and Switched live (Y) to Call for heat. [The Heating
Satisfied terminal is not used in this application - but could be in some -
or could be used if you were controlling a cooler rather than a heater].

HTH.
--
Cheers,
Set Square
______
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