new room stat to be fitted ... 2 wire/3 wire

[loveplumbing]

Hi all

I have bought a new room stat today to replace my old tatty one

a normal room stat (not a prog or wireless type!)


my old room stat is acl and i have bought a sunvic

i know my old room stat had 3 wires and the sunvic one i have has 3 terminals 2: 1, 2 & 3

(although on the box it says it is a 2-wire design!!

it has a disgram too which should be easy to follow

basically do i just swap them over, ie/ the common terminal, the call and the satisfied terminal. (i will work out which is which from the disgram and also if need be by looking into the junction box and possibly by using a multimeter.

basically what i want to know is: is a 2-wire room sat OK to replace a 3-wire room stat ??

 

[liverpoolboy]

Hi

Most room stats have 3 wires, some do have a neutral wire also though.

if your room stat has 3 wires then they will usually be C (common) demand and sat

you can only replace a room stat that requires a NEUTRAL wire (so usually 4 wires) with another room stat that also accepts a NEUTRAL wire (4 wires)

Some stats only use 2 wires but it's advisable to replace a room stat that requires 3 wires (as above) with another that also requires 3 wires .

 

[twgas]

your queries were answered on a previous thread - do you think something may have changed?

and have you sorted your 3-port valve problem

 

[D_Hailsham]

if your room stat has 3 wires then they will usually be C (common) demand and sat

When did you last see a stat which had a wire connected to the sat terminal?
If the stat has three wires they will invariably be Live, Switched Live (Demand) and Neutral

you can only replace a room stat that requires a NEUTRAL wire (so usually 4 wires) with another room stat that also accepts a NEUTRAL wire (4 wires)

Rubbish.

Some stats only use 2 wires but it's advisable to replace a room stat that requires 3 wires (as above) with another that also requires 3 wires .

Why? Depends on what the three wires are! If they are live, switched live and neutral, and you buy a digital stat, 99 times out of 100 the neutral will be redundant. It is only required on mechanical stats to make the anticipator work. Digital stats so not need an anticipator, so no neutral.

PS to OP

What make/model are your old and new stats?

 

[liverpoolboy]

so D_Hailsham: you are saying most if not all modern digi stats only have 2 wires and no neutral wire?

i apologise by 3 wires usually found in the stat it is usually: Common wire (Neutral) and the other two close to make (demand).

 

[D_Hailsham]

so D_Hailsham: you are saying most if not all modern digi stats only have 2 wires and no neutral wire?

i apologise by 3 wires in the stat it is usually: Common wire (Neutral) and the other two close to make (demand).

1. A digital stat may require a neutral if the display is powered from the mains but, if it is powered from a battery, there will only be two terminals. These can be used either to switch 240v mains or as "volt-free" terminals connected directly to the boiler

2. Common and Neutral are NOT the same thing.

Mechanical stats often had 4 terminals: Common, Call, Satisfied, Neutral. 240v would be connected to the Common from the Timer CH ON terminal and the Neutral connected to the mains neutral. The boiler would be connected (via motorized valve) to the boiler. If the temperature is below that set on the thermostat, the Common and Call terminals would be in contact so the mains 240v would turn on the boiler. When the set temperature is reached, the contacts switch over so the Common and Satisfied terminals are in contact. In normal circumstances there is nothing connected to the Satisfied terminal, so the boiler switches off.

The satisfied terminal can be used in cooling and air conditioning applications.

 

[liverpoolboy]

hmm interesting..
from the ones i have seen (mechanical room stats) and from the y plan wiring diagrams the NEUTRAL terminal goes to the stat and there are two other terminals that make or break - one of these is linked to the programmer HTG terminal - so (3 wires in total).

 

[D_Hailsham]

from the ones i have seen (mechanical room stats) and from the y plan wiring diagrams the NEUTRAL terminal goes to the stat

That's right; it's there to make the anticipator work.

there are two other terminals that make or break - one of these is linked to the programmer HTG terminal - so (3 wires in total).

That's also correct. The wire from the Programmer will be connected to the Common terminal; the other will go to the motorized valve/boiler.

 

[liverpoolboy]

what exactly the aticipator for? how does the neutral wire do this/make it work?!

 

[D_Hailsham]

what exactly the aticipator for? how does the neutral wire do this/make it work?!

Mechanical stats have a fairly large temperature difference between make and break, sometimes greater than 3°C, which would be noticeable.
The anticipator is a resistor between Call and Neutral terminals. When the thermostat is calling for heat, current passes through the anticipator, so the inside of the thermostat warms up. This means that the stat will turn of slightly earlier and thus reduce the temperature difference between on and off. This means the differenc ereduces to about 1°C, which is not noticeable.

 

[namsag]

to anticipate .

 

[loveplumbing]

thanks everyone for your views/info.

ok my stat is a sunvic TLX 4101

it has a small info leaflet with it and it gives details on other room stats for when wiring

the sunvic i have has common (2) dem. (1) and sat. (3)

my old ACL TS142, according to the leaflet has; common (1) dem. (2) and N/A for sat. but N (4)

I take it N means neutral, as mentioned and discussed in the posts prviously.

how do i go about replacing - i mean should i have bought a different stat with N connection too?

as my new sunvic has 3 terminals as well as my old one, but with my old one has a N terminal and my new one having a SAT. terminal instead of the N. can these just be swapped??

sorry if this sounds very confusing to you.....

 

[twgas]

disconnect N (as you say, neutral) at both ends and make safe,

com = com

dem = dem

 

[loveplumbing]

disconnect N (as you say, neutral) at both ends and make safe,

com = com

dem = dem

Hi there again

Right am off this afternoon and am going to replace it now finally!...

the new stat also has a third terminal SAT but i just leave/ignore this terminal i believe ... (correct me if a am wrong please)!

so the common terminal goes to 2 on my new stat (1 on the old one) and demand to 1 (2) on my old one.

 

[D_Hailsham]

the new stat also has a third terminal SAT but i just leave/ignore this terminal i believe

Yes, ignore the SAT (3) terminal

so the common terminal goes to 2 on my new stat (1 on the old one) and demand to 1 (2) on my old one.

Correct.

Make the unused N wire safe at both ends.

Happy wiring.