Swapping a T6360B for a HC60NG thermostat

[Mrak]

Hi,

My heating and hot water is on a old sundial plan (does that make it an S plan?). I've already swapped the ST1000 programmer for a ST6400C without any problem. Now because the 'stat is about 2 foot away from the hot water tank I was planning on swapping it for a wireless version, the HC60NG. Being naive I thought that it would be a straight wire for wire but that doesn't appear to be the case.

This is where I turn dumb. the old stat was marked up 1,2 and 3. and the new one, ignoring the permanent power feed is A,B and C. What goes where? Originally 1 connected to 4 (CH on?), 2 to 2 (Neutral) and 3 to 5 (White wire on the mid position valve). I can't see a diagram for connecting to the sundial wiring center.

Best guess at the moment is that A should go to 4 and B to 5 which leaves the neutral on 2 spare?

Any advice appreciated before my head explodes.

 

[D_Hailsham]

does that make it an S plan?

Not necessarily. S Plan uses two 2-port motorized valves; Y Plan uses one 3-port valve

I was planning on swapping it for a wireless version, the HC60NG.

The HC60NG is just the relay unit; the thermostat is the other part!

Presumably you are just installing a wireless thermostat and not a programmable wireless stat, so keeping the ST6100 as the programmer for CH and HW.

Originally 1 connected to 4 (CH on?), 2 to 2 (Neutral) and 3 to 5 (White wire on the mid position valve).

Best guess at the moment is that A should go to 4 and B to 5 which leaves the neutral on 2 spare?

Good Guess! The neutral is not used. You will of course need a permanent live and neutral to the L and N terminals. Do not link L to A.

 

[Mrak]

Thanks for that. Definitely a Y plan then, it uses a 3 port valve. Yes, definitely keeping the programmer, the reason why I went for the HC60NC and HCW80 is that they appear to be one of the most simplistic.

Out of interest, what does the neutral feed to the original 'Stat do? Using my multimeter there appears to be no continuity between any of the other connectors on the stat irrespective of the dial position. The circuit diagram shows some sort of sine wave but I have no idea what this means?

 

[D_Hailsham]

Out of interest, what does the neutral feed to the original 'Stat do? Using my multimeter there appears to be no continuity between any of the other connectors on the stat irrespective of the dial position.

The neutral is there to complete the circuit for the anticipator resistor. This is a small resistor connected between terminals 2 and 3 of the thermostat. When the thermostat is calling for heat this resistor is in circuit and warms up slightly. The purpose of this is to reduce the hysteresis of the bimetallic temperature sensing element in the thermostat.

Modern, digital thermostat use thermistors to measure the temperature, which do not require an anticipator.