Wiring RF Stat to Unica HE 32

[ntl142]

Hi all, I've got an RF room stat and want to wire it to my boiler. I'm 99% sure I've got the right plan, but would like a sanity check before I switch it all on.


The boiler is a Unica 32 HE. Manual here, and pages 27 and 28 are the relevant ones:
http://cdn0.vokera.co.uk/wp-content/uploads/2009/04/unica-he-installation-and-servicing-manual.pdf

My boiler currently has a mechanical clock installed, which I've confirmed is wired as per Fig 39 on page 27.


The RF stat is a Siemens RDJ10RF. Manual here, with page 10 showing the wiring diagram.
https://w3.siemens.co.uk/buildingte...ocumentation/Documents/RDJ10RF Data Sheet.pdf

Siemens video here, relevant bit at 3.26 (24v wiring) or 3.39 (240v wiring).

Here is a photo of the current boiler wiring with mechanical clock:

http://tinypic.com/r/124ioaq/9

And the clock itself:

http://tinypic.com/r/k0r81l/9


I've removed the clock (black switch wires to A and C, and power from D and E).

I've got an isolated L and N feed for the stat from outside the boiler, so that's fine.

Assuming* it's 240v wiring I need to bridge L and Lx in the stat (according to the video), so that's fine too.

I then need to connect L1 in the stat to somewhere in the boiler. This will either be A or C on the M5 block.

I think L1 goes to A - can anyone confirm or tell me I'm wrong please?

I'm a bit confused because the current clock closes/opens a switch between A and C on M5. The new stat looks like it only has one wire to A (or C?). Is that where the link/bridge between L and Lx in the stat comes into it, i.e. the live feed comes from the mains into the stat, and then is fired out into A?

How can I confirm I need to wire the stat for 240v and not 24v? The boiler manual doesn't explicitly say. I'm going off the fact that the mechanical clock was 240v, and the stat is simply replacing the clock. However, there is also a loop on M3a in the 24v part of the box. Again, 99% sure it's 240v but would appreciate a sanity check before I commit!

Thanks a lot in advance!

 

[stem]

Its pretty much a like for like swap.

The black wires from the existing timer are the switching contact wires as you have figured. Remove them both from the boiler terminal block and where they came from run wires to the contacts at the Siemens receiver which are terminals Lx and L1 (it doesn't matter which way around they are, nor does the switching voltage matter as the contacts are potential free)

Finally you need to get a 230V live and neutral supply to the Siemens receiver and that's it. This should come from the same 3A fused connection unit as the boiler, so that the one switch removes power from the boiler and the Seimens receiver.

No links required.

 

[ntl142]

Thanks, that sounds really clear. When I initiially thought it through that's what I would have done too - the new Siemens controller/stat is a switch just the same as the mechanical clock.

So why does the Siemens video show wiring for 24v and 240v? And if mine is 240v (99% sure it is), why don't I need the link (L to Lx) like they show in their video? Not doubting you, just trying to understand because a lot of info seems conflicting to me.

I think this might be the critical bit that I'm not fully understanding "it doesn't matter which way around they are, nor does the switching voltage matter as the contacts are potential free."

Thanks again.

 

[stem]

Sometimes where 230V is switched, there are only 3 wires used, so a link must be made between the live that provides power to the thermostat and one side of the switching contact, the second wire is the switched live from the other side of the contact that goes to operate the boiler, and the third wire is the neutral.

In your case there are 4 wires, 2 that are for the switching and 2 that are the 230V to power the thermostat.

Looking at the circuits for your boiler it would appear that the switching voltage is 24v and so two separate wires are provided (a supply out and a return to the boiler) If you had gone ahead and wired it up with a link, then you would have applied 230v to your boilers 24v circuit and probably blown up the boiler PCB. So well done for checking before you proceeded.

Basically Lx and L1 are just two contacts that are connected together when the thermostat switches 'on' they are not connected to any source of power internally and so are described as 'potential (or voltage) free' they will switch whatever voltage is applied to them. Within their operating range of course.

Edit
If you want to know how to know your boiler uses 24v for the control circuits, see the manual you posted page 15 figure 18, which identifies the terminals to which the thermostat switching wires are connected as 24v and, also the requirement to have a voltage (or potential) free time clock as per 8.2 on page 27.

 

[ntl142]

Hi again, thanks a lot, really appreciate your assistance.

What was it that made you think it's a 24v switching circuit in the boiler? I'm keen to learn. The current mechanical clock has a 240v feed and the switching circuit is on the M5 block which is in the 240v compartment in the circuit box. Tracing the wiring from this goes to CN1 on the main board, which is described as 'connection to PCB high voltage'. Chunky wires too (red and black in the photo I posted earlier).

The 24v compartment is identified as M3a and M4 and is not connected to the current mechanical clock. These are connected to X9 and X2 respectively which is described as a 'connection to PCB low voltage' in the boiler manual. Skinny wires between M3a and X9, and M4 and X2.

This is all based on Fig 38/page 28 of the manual, and my photo above, and I *think* I'm interpreting it right:
http://cdn0.vokera.co.uk/wp-content/uploads/2009/04/unica-he-installation-and-servicing-manual.pdf

It was this doubt that made me ask on here! Haha.

Could I verify the switching voltage by putting a multimeter on A and C (the two black wires on connector block M5) and testing for 24v or 240v when there is a call for central heating?

 

[stem]

Sorry I must have edited it after you read my last post.

If you want to know how to know your boiler uses 24v for the control circuits, see the manual you posted page 15 figure 18, which identifies the terminals to which the thermostat switching wires are connected as 24v and, also the requirement to have a voltage (or potential) free time clock as per 8.2 on page 27.

Are you now saying that the black wires [1 & 4] from the clock didn't go to the 24v terminals [M5 block] as shown in the manual? You originally said that it was connected as per fig 39 page 27

Not that it matters really anyway, because you are swapping like for like, and if it worked before it will work after the exchange.

 

[stem]

Sorry I omitted to comment on

Could I verify the switching voltage by putting a multimeter on A and C (the two black wires on connector block M5) and testing for 24v or 240v when there is a call for central heating?

No it's not that simple unfortunately. It doesn't work like that. The two wires will have the same voltage. Remember they are connected to a switch when the switch is 'on' the two wires will simply be connected together and therefore at the same voltage, there will not be a voltage difference between them to measure.

 

[ntl142]

Think there might be some crossed wires here - sorry about that! This photo shows the wiring in the boiler without me doing anything to it, i.e. mechanical clock still installed. This is the clock I want to remove and replace with the RF stat. The question seems to be whether I should install the stat as 24v or 240v.

http://tinypic.com/r/sw39k2/9

• The big red box on the right goes around M3 (240v input, L N and E) and M5 (2x black, 1x blue, 1x brown). Fig 38/page 28 shows this to be 'connection to PCB high voltage' connecting to CN1 on the board.

• The big blue box on the left goes around M4 (nothing out the top site) and M3a (small black wire loop). Fig 38/page 28 shows this to be 'connection to PCB low voltage' connecting to X2 and X9 on the board.

This fits in with fig 18 on p15.

The clock is only connected to things in the red box. I am assuming this is all 240v in here (correct?). The power to the clock appears to come from the brown and blue wires you can see in M5. The black wires from the clock (1 and 4) go to M5 also. The clock isn't directly connected to anything in the green box.


You said: Are you now saying that the black wires [1 & 4] from the clock didn't go to the 24v terminals [M5 block] as shown in the manual? You originally said that it was connected as per fig 39 page 27.

I did originally state that the clock is connected as per fig 39 on p27, and I stand by that. I don't think I've said anything to counter that - apologies if I've worded anything poorly. The clock is wired to M5 as shown in the photo. I am 100% sure that I have labelled M5 correctly in my photo because there is a label on the underside of the lid (just visible in the photo) saying it is M5. Just to the right of that label is another one (obscred by the latch) saying M3 and showing mains input.



Thanks for clarifying the voltage measurement wouldn't work. I wondered if I would be measuring the voltage over the clock, but as you've said it is just a switch so that won't work.

 

[stem]

Thanks for the photo. It's 24v

The black wires from the existing clock that go to the red and black boiler wires are in the M5 terminals, so are 24v. This is for the control circuits. The boiler will generate this 24v internally. Remove the black wires from the clock and connect the terminals to the Siemens Lx and L1.

In addition to the 24v, the new thermostat receiver needs 230v to power it. If you remove the L & N wires from the adjacent terminals that are going to the existing clock you can use them for the L & N to power the Siemens receiver, so my first post is correct.

The black wires from the existing timer are the switching contact wires as you have figured. Remove them both from the boiler terminal block and where they came from run wires to the contacts at the Siemens receiver which are terminals Lx and L1 (it doesn't matter which way around they are, nor does the switching voltage matter as the contacts are potential free)

Finally you need to get a 230V live and neutral supply to the Siemens receiver and that's it. This should come from the same 3A fused connection unit as the boiler, so that the one switch removes power from the boiler and the Seimens receiver.

No links required.

 

[ntl142]

Awesome, thanks for the clarification - much appreciated. I'll get it wired in when I have time later in the week and let you know how I get on.

 

[stem]

You're welcome. It helps any that follow when searching for the same thing in the future if you post how you get on.

Just make sure that the L & N mains supply to the existing clock are actually the brown and blue wires that go to the terminals at the right of the black wires, they look as if they are, but I can't see them 100% in the photo. If the are, they will be the ideal supply for the Siemens receiver.

Also, as you only mention the existing timer, and you haven't mentioned the presence of any existing room thermostat, I've assumed that presently you don't have one. If you do it will need removing and a small wiring modification.

 

[ntl142]

No existing room stat, just the mechanical clock. I've wired in another external source for the receiver so I'll use that - the Siemens manual recommended it. Couldn't see the point, but done it now anyway. Thanks.

 

[stem]

The receiver should be connected to the same 3A fused connection unit as the boiler. So that the same switch isolates both the boiler and any accessories connected to it. In your case the receiver.

I don't see any such recommendation to wire the receiver to a different source in the Siemens manual you have posted.

Edit
your boiler manual states on page 27 under external wiring "If external controls are to be added to the system, they must be connected to the appliance as shown in the following diagrams" The diagrams referred to all show the external controls connected to the same 230v supply as the boiler.

 

[ntl142]

It's all up and working now. The switching circuit was indeed 240v as I initially thought and the manual implied. I checked that the mechanical clock acted only as a switch and didn't supply any power, and that the Siemens stat operated in the same way. It all tied up, so I wired it in and it's working fine now. Thanks for all your comments, it's helped me to align my thoughts and learn a bit along the way too.

Out of curiosity, could I have wired it up as per the 240v option in the Siemens video? As long as the single wire from the switch on the new stat went to the correct one of M5-A and M5-C, would it have worked? The Siemens stat would then have not needed the 240v supply from the switching circuit on the PCB, but would have used it's own 240v supply to put back into the switching circuit. Would that work?

 

[stem]

Glad to hear it's working. Well done!

The switching circuit was indeed 240v

I think you mean 24v

And no you can't wire it up as 230v. If you were to have done, you would have put 230v mains on a circuit designed to operate with 24v, or nearly 10 times its designed voltage.... I'll let you work out the possible consequences of that.....