wiring a 24v thermostat with a twist

[stem]

Based on the limited information you have given, I have made a sketch of how I understand the Aube RC840T is wired. Unfortunately saying that..

The boiler has a 4 core but unsure how these are connected internally

Is not very helpful. This information is essential, because methods of wiring, boiler requirements etc., change from installation to installation, depending upon the connected components and who installed it.

Most boilers require a permanent live, a switched live (that starts the heating running) and a neutral. The Aube provides these, but you will need to find out the correct connections for these at the boiler end.

The same is true of the thermostat. The Aube unit provides 24 VAC control signal, you will have to confirm that this is suitable for the Nest and what terminals to connect to.

Finally, there is no mention of a timeswitch, so I assume the 'Nest' can provide time control as well as temperature control.

Taking into account other comments regarding motorised valves. There isn't any wiring for one shown in your photographs, and as not all systems have one it's likely there isn't one. However if there is some wiring for one elsewhere that changes everything.

Untitled

• stem
• 21 Jun 2013
• 1

 

[matt1e]

Stems sketch above looks ok the colours are
blue = neutral
black = line
red = S/L
but it is only ok if your boiler is currently switched directly via the thermostat at line level.
as others have mentioned there may be other components in the system and also as has also been mentioned the unit is designed to switch resistive heating loads ie elements not boilers (its overkill)

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• simmo490
• 20 Jun 2013
• 1

looking at your Pic above it seems as though you have a actual switched pair coming from the boiler (the black and grey) they are sleeved brown so one would expect them to be at line potential but are you sure they are?
just because your room stat is rated at 240v it doesn't mean it is switching at that level
what make and model is your boiler ? as many are designed to use either a switched live or a ELV pair nowadays

Matt

 

[ban-all-sheds]

just because your room stat is rated at 240v it doesn't mean it is switching at that level

I don't know what percentage (it'll have lots of 9s in), but most boilers in this country need volt-free programmers

 

[matt1e]

I don't know what percentage (it'll have lots of 9s in), but most boilers in this country need volt-free programmers

Sorry, I disagree with that Bas

Matt

 

[ban-all-sheds]

OK.

I am surprised though, I thought non volt-free went out decades ago. What do you think is wrong, "most", or "lots of 9s"?

 

[matt1e]

OK.

I am surprised though, I thought non volt-free went out decades ago. What do you think is wrong, "most", or "lots of 9s"?

Both to be honest,but I can only speak from experience,and also the fact that I work in the commercial HVAC sector probably blinds me to what is getting to be the norm where domestic boilers are concerned.
discounting the use of 0-10v, 4-20mA,open-therm or similar control I find the only other option is usually switching at line voltage.
domestic boilers (again discounting OT etc)I usually find either S/L or voltfree, or the choice of either
but I wouldn't say there were more than one over the other, but again I'm not the best one to comment on domestic boilers,perhaps one of the domestic installers on here could comment?

Matt

 

[stem]

Regarding my drawing, when you said..

but it is only ok if your boiler is currently switched directly via the thermostat at line level.

That was the point I was trying to make by making the following comment about the wiring to the boiler;

This information is essential, because methods of wiring, boiler requirements etc., change from installation to installation

Sorry it wasn't clear.

 

[ban-all-sheds]

Simmo seems to have lost interest...