Thermostat help!

[DaveStewart]

Evening all,

I currently have a Hortmann HRT" thermostat which is temporamental! It has 3 wires into in - live "load" and neutral. I've just bought a Siemens RAA20 to replace it, but the instructions show only 2 wires, seemingly live and neutral...

Is it possible to wire this thermostat up with the 3 wires, or should i take it back and exchange it?

Many thanks in advance

Dave

 

[Softus]

It has 3 wires into in - live "load" and neutral. I've just bought a Siemens RAA20 to replace it, but the instructions show only 2 wires, seemingly live and neutral.

The two wires are 'live' and 'switched live'.

Is it possible to wire this thermostat up with the 3 wires, or should i take it back and exchange it?

It's fairly straightforward.

The principle is to make safe the neutral wire and not use it.

To achieve this you need to identify the correct wire. There are three alternative methods:

1. Guess.
If you post here with the insulation colours of the three wires, it might be possible to help you make an educated guess, but this isn't the best way of going about it.

2. Deduce.
Having isolated the power, look at the connections on the existing thermostat, and write them down. Determine which one is neutral.

3. Analyse
Having isolated the power, find the other end of the thermostat flex/cable, and determine the function of each wire from the connections to the other system components.

Of the above methods, I recommend the second one. If you can't interpret the thermostat markings, then just ask here.

Having determined which is the neutral wire, put it into a connector block and don't use it with the new thermostat.

Tip: Don't assume that the neutral conductor is the blue one.

 

[DaveStewart]

Many thanks for that!!
The instructions for the old thermostat wiring can be seen here:


www.screwfix.com/sfd/i/cat/pdfs/07/p3133907.pdf

From this, I assume the wire in block 4 would be neutral?

Many thanks...

 

[Softus]

Quite so. Disconnect (4) and make it safe.

The wire at (1) should be the live, and the one at (3) should be the switched live.

PS How's Annie?

 

[DaveStewart]

Many thanks!

And the last I heard Annie's fine, haha! - WishI had the money of my namesake...

Thanks

Dave

 

[Softus]

You're abundantly welcome.