neutral wire in roomstat

[ant101]

Im studying a diagram of a programmer(horstman C27) and also a roomstat diagram (Honeywell T6360B).
The programmer instructions show CH wire going to roomstat (C terminal), with a choice of switching to (CALL OR SAT)...This I understand.
Coming of the CALL terminal is a zig zag wire (resister maybe) going back to neutral (what is this for? and would it work if the wire was not connected ?).

The roomstat diagram shows terminal 2 and 3 connected by the zig zag wire, C, heating load and neutral. similar to above.

I would be gratefull for a simple explanation.
thank you,
student.

 

[breezer]

some room stats do require a resistor to heat (slightly) the bimetal strip, hence they need a neutral

 

[picbits]

Some room stats are semi intelligent i.e. they have electronics in them.

A simple (older) stat was just a bimetallic strip which turned on and off depending on heat.

On newer electronic thermostats they have electronictrickeryjiggerypokery in them which requires powering. The live and neutral to the stat provide this and they generally provide a switched live output via a relay or triac to signal that heat is required.

 

[simond]

As far as your question wording is concerned, Breezer has given the correct answer.

The heater is there to reduce hysteresis; that is to make the temperature response of the thermostat in relation to the room temperature more consistent, without peaks and troughs.

In a few electronic stats, a neutral is used but this is unusual as most modern units use a battery to power the electronics and the volt free relay.

The electronic stats are generally more accurate because they use an electronic temp sensor (thermistor) and the hysteresis problem is normally handled by software.

 

[ant101]

Thanks for your answers everybody,
Sorry my reply is late,
Very helpful
Thanks