Wiring for New Room Thermostat

Hi

I have looked through the forum to try and find an answer to my question, but I couldn't find what I needed, hence this post.

I would like to replace my old mechanical Drayton room thermostat with a new digital Heatmiser DS1-L, but I would like confirmation on the wiring...

Drayton Wires are as follows as per diagram on inside of cover:

3 - Yellow = “Cooling Load”
2 - Yellow = “Heating Load”
1 - Red = “Accel”
4 - Neutral - Blue

Heatmiser Wiring Diagram as follow:
L - Live
N - Neutral
A1, A2 – Heating Connection

I think I am ok with the following (No earth required on this stat I assume)
Red (Live) = L
Blue (Neutral) = N

But I am unsure what should be happening with my two yellow wires and the supply to A1 & A2

When I went to Heatmiser's website and checked the wiring diagram it says something extra:-
"For 230v switching, you need to link from L to A1 and then connect your switch wire to A2", which I assume this means I put a new wire from L to A1.

BUT WHERE DO MY EXISTING TWO YELLOW “COOLING LOAD” & “HEATING LOAD” WIRES GO?

Many thanks in advance.

The Heatmiser stat is a zero volt switch which means although you have 240v to the stat is does Not put that to the switched output terminal A2. All it does is switch whatever you have on input terminal A1 to output terminal A2. So in answer to your question, yes, if you want it to switch 240v out, then that is what you have to put onto the input switch terminal A1, so you make and connect a link from L to A1.
Your Yellow wires I know nothing about and it sounds like its very specific to your installation and therefore you may need something more than just switching live via the Heatmiser.
Maybe someone else can help on the yellow wires.....

It sounds like your heating system may need the wall thermostat to put Live on the Heating Load when the room needs heating and possibly put Live on the Cooling Load when the room is too warm ( assumes there is a cooling or air conditioning function in the system.

Or the heating system needs the thermostat to put Live on ""Cooling Load"" when the room does not need heating so that the system can use the boiler to heat water in the tank if that is necessary.

So more details of the boiler / heating system is needed.

Thanks for the responses........

The boiler is a "Vaillant ecoTEC Plus 428 Regular Boiler" just serving to heat the central heating and water, no air con or cooling.

The boiler was installed 18 months ago and the Drayton thermostat I'm trying to replace wasn't touched at all during installation of the new boiler.

It sounds like you have a Y-plan.. if so you will need the NO & NC contacts in the roomstat for the valve to work properly.

nozspark said:

It sounds like you have a Y-plan.. if so you will need the NO & NC contacts in the roomstat for the valve to work properly.

Click to expand...

In other words, it's unlikely you'll be able to use the stat you have purchased with your system, short of adding extra external components, which would be a lot of hassle.

nozspark said:

It sounds like you have a Y-plan.. if so you will need the NO & NC contacts in the roomstat for the valve to work properly.

Click to expand...

So if I get a room stat with the above contacts, which yellow goes to which or is it not that simple?

it won't be a Y plan as that only needs a call for heat wire to the valve.
without knowing what system you have it is difficult to say but some types of valve need to be driven open for heating and closed for off unlike honeywell which spring closed.
look at valve(s), how many ? one 3 pipe / two 2 pipe, makers name model.
The valve(s) are controlled by room/tank stats which in turn call boiler/pump so as much info as poss. please