/ Boiler RF Thermostat wiring

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NottsRich on 03 Oct 2017
Hi all, I've got an RF room stat and want to wire it to my boiler. I was 99% sure I had the right plan, but have now been given some more conflicting information so need to clarify it.


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/buildingtechnologies/uk/en/building-automation/residential-controls/documen...

Siemens video here, relevant bit at 3.26 (24v wiring) or 3.39 (240v wiring).
https://www.youtube.com/watch?v=O0pTT3qSejc

Here is a photo of the current boiler wiring with mechanical clock still installed:
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 in my photo above).

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

I need to be able to confirm if I wire it up for 24v or 240v, but have been given conflicting information.

How can I confirm if I need to wire the stat for 240v or 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, I've also been told that the red and black wires into M5 are 24v not 240v, so I'm pretty confused - this seems to contradict the boiler manual. Keen to learn so will try to figure it out before paying someone to do it. Any advice much appreciated! Thanks.
marsbar - on 03 Oct 2017
In reply to NottsRich:
Can you borrow a multimeter and check the existing one?

Also if you look at page 15 of the boiler manual you will see fig 18 shows you which is 24 and which is 240. Compare that with where your wiring is for the old one.

Fig 39 and 40 also suggest 230v.

Who told you otherwise?

(It goes without saying that if you are not sure you probably shouldn't be messing with it.)

Do you have an existing wired room temperature dial? This may need removing and could be wired in somewhere difficult to find.
Post edited at 21:01
NottsRich on 03 Oct 2017
In reply to marsbar:

I have a multimeter, but unsure how to check if the current timeclock switches 24 or 240v. Done plenty of automotive/DC circuit work, but AC is relatively new to me. Wiring in lights etc is fine, but mains voltage PCBs are new. Just want to make sure I'm correct before I proceed. Thanks for the warning.

"Also if you look at page 15 of the boiler manual you will see fig 18 shows you which is 24 and which is 240. Compare that with where your wiring is for the old one."

Yes, I've done that. The clock is wired into the 240v section. The manual implies that M5 is connected to CN1, i.e. the PCB high voltage side. Other connections M3a and M4 are connected to X1 and X9 which are low voltage PCB connections. Everything points to it being 240v, except someone who apparently knows what they're talking about, who says that I should be wiring it up as 24v as 240v would blow the board. I now need to triple check everything to make sure it's not an expensive mistake!

No, there's no existing thermostat, hence fitting this one. Just a clock.
gethin_allen on 03 Oct 2017
In reply to NottsRich:
All the new timer/thermostat is doing is switching, it doesn't supply any current to the boiler, the 230v to the rf base station is just a supply for it to receive and process signals from the timer/thermostat. If you set your multimeter to the correct settings and measure what your current mechanical clock is switching you can see what that's switching and then if your new rf base station is happy switching this voltage then there's your answer.
Edit.
I'd say the answer is in fig. 19
Post edited at 22:58
gethin_allen on 03 Oct 2017
In reply to gethin_allen:
Looking at the diagrams in the Siemens manual it appears that be used to supply a current to a boiler or pump, you don't want this, you just want what is effectively a fancy switch that when the room thermostat/controller wants to turn the heating on/off is closed or opened.

Only do this if you understand what I'm blabbering on about and be very careful with any live connections.

Connections Lx and L1 on the base unit are shown as being switched and according to the thermostat spec sheet will switch anything from 24-250v.
To test this, If you wire up terminals L and N to the 230v fused supply and then with the thermostat in the OFF (no heating demand position) test both the continuity and voltage across the Lx and L1 termini, this should show no voltage and an open circuit.
If you then switch the slider to constant heating demand (slider 16 in the diagram) or press the override button on the base station this should result in a closed circuit between termini Lx and L1 but no voltage.
If this is the case, check your mechanical clock you removed that when in the off position the circuit between the black termini is open and in the on position the circuit is closed.
If all is as stated I'd connect the Lx and L1 termini of the thermostat to M5 A and C on the boiler, Lx to whichever of A or C is live and L1 to the one that is return/neutral.
Saying that I'd do this does not mean that you should if you don't understand my logic for suggesting this. Obviously I can't take any responsibility if you mess things up.
Post edited at 23:59
marsbar - on 04 Oct 2017
In reply to NottsRich:

I'm not the best person to explain the multimeter sorry I have to ask him indoors to remind me most of the time.

If you don't have a thermostat already that's easier.

I reckon it's just shove it in to the 240 volt side but new pcbs are expensive so you need to decide if it's a gamble you are willing to take. I'm not qualified I'm just some random on the Internet. At least if you pay someone to do it they will have to get it right or buy you a new board if they don't.
NottsRich on 04 Oct 2017
In reply to gethin_allen:

> All the new timer/thermostat is doing is switching, it doesn't supply any current to the boiler, the 230v to the rf base station is just a supply for it to receive and process signals from the timer/thermostat.

Agreed, it should make/break a switch to call for heat or not. The mains supply powers the receiver/base station. Why then, in the video I linked to in my OP, does it offer two ways of wiring it up? 24v or 240v. The 240v option takes a live from the power supply to the receiver and sends it to the boiler. If I choose this method and it's wrong, it will fry my PCB.


> If you set your multimeter to the correct settings and measure what your current mechanical clock is switching you can see what that's switching and then if your new rf base station is happy switching this voltage then there's your answer.

This is what I want to do. Does this method make sense?

Isolate boiler.
Disconnect black wires from M5 and hang somewhere safe.
Set clock to off.
Turn on boiler.
Measure voltage with a multimeter by touching a probe onto each of the black wires. Should read 0.
Set clock to on.
Measure voltage with a multimeter by touching a probe onto each of the black wires. Should read 24 or 240v.


> I'd say the answer is in fig. 19.

Yes, that's what I thought originally. It shows that the new stat should be connected to M5. The current mechanical clock is connected to M5, so I would replace one with the other. That's ok. It's the wiring in the stat I'm not certain about now due to an 'expert' giving me some doubt. What I mean is referred to in the video in the OP at 3.26 (24v wiring) or 3.39 (240v wiring).

NottsRich on 04 Oct 2017
In reply to gethin_allen:

> Looking at the diagrams in the Siemens manual it appears that be used to supply a current to a boiler or pump, you don't want this, you just want what is effectively a fancy switch that when the room thermostat/controller wants to turn the heating on/off is closed or opened.

> Only do this if you understand what I'm blabbering on about and be very careful with any live connections.

> Connections Lx and L1 on the base unit are shown as being switched and according to the thermostat spec sheet will switch anything from 24-250v.

> To test this, If you wire up terminals L and N to the 230v fused supply and then with the thermostat in the OFF (no heating demand position) test both the continuity and voltage across the Lx and L1 termini, this should show no voltage and an open circuit.

> If you then switch the slider to constant heating demand (slider 16 in the diagram) or press the override button on the base station this should result in a closed circuit between termini Lx and L1 but no voltage.

> If this is the case, check your mechanical clock you removed that when in the off position the circuit between the black termini is open and in the on position the circuit is closed.

> If all is as stated I'd connect the Lx and L1 termini of the thermostat to M5 A and C on the boiler, Lx to whichever of A or C is live and L1 to the one that is return/neutral.

> Saying that I'd do this does not mean that you should if you don't understand my logic for suggesting this. Obviously I can't take any responsibility if you mess things up.

This all makes sense and is similar to what I had thought too - thanks. I want to verify if 0, 24 or 240v is going through the black clock wires when it switches. If 0 or 24 then I do the normal wiring for a simple switch (at 3.26 for 24v wiring in the video). If 240v then I wire as per 3.39 (240v wiring) in the video.

The video shows something that's not included in the wiring manual for the thermostat, so it's adding a layer of confusion.

3.26 (24v wiring) or 3.39 (240v wiring).

NottsRich on 04 Oct 2017
In reply to marsbar:

> I reckon it's just shove it in to the 240 volt side but new pcbs are expensive so you need to decide if it's a gamble you are willing to take.

It wasn't a gamble to start with, I was certain about the wiring. I'm now in doubt due to an 'expert' advising differently. Frustrating! I need to be certain before I carry on.
gethin_allen on 04 Oct 2017
In reply to NottsRich:
"> This is what I want to do. Does this method make sense?

> Isolate boiler.

> Disconnect black wires from M5 and hang somewhere safe.

> Set clock to off.

> Turn on boiler.

> Measure voltage with a multimeter by touching a probe onto each of the black wires. Should read 0.

> Set clock to on.

> Measure voltage with a multimeter by touching a probe onto each of the black wires. Should read 24 or 240v."

This is a good plan of attack but, my guess is that you will not have any voltage across the black terminals with the clock in either on or off positions but, if you use your continuity tester you will have an open circuit with the clock in the off position and a closed circuit with the clock in the on position.

Just to add that table 7.12 in the boiler manual indicates that the room thermostat is a 230v. If you power up the boiler with the mechanical clock removed and check the voltage between A and C on block M5 it should be 230V

And fig 40 in the boiler shows the thermostat and programmable timer as two components which are both included in the siemens RF thermostat and connection b in block M5 as a dead end (just to put the thermostat in line between the programmer and the boiler.
Post edited at 14:59
NottsRich on 04 Oct 2017
In reply to gethin_allen:
> This is a good plan of attack but, my guess is that you will not have any voltage across the black terminals with the clock in either on or off positions but, if you use your continuity tester you will have an open circuit with the clock in the off position and a closed circuit with the clock in the on position.

I had the same thought after I wrote that - no voltage in the 2 black (clock) wires. So if I understand you correctly, I'll measure voltage on the black and red wires coming into the bottom of M5 at A and C - right?

> Just to add that table 7.12 in the boiler manual indicates that the room thermostat is a 230v. If you power up the boiler with the mechanical clock removed and check the voltage between A and C on block M5 it should be 230V

Hadn't spotted that table, thanks for that. To test this, it seems to be the same as what you wrote above, i.e. testing voltage across A and C with clock disconnected.

> And fig 40 in the boiler shows the thermostat and programmable timer as two components which are both included in the siemens RF thermostat and connection b in block M5 as a dead end (just to put the thermostat in line between the programmer and the boiler.

Yes, it fits that the Siemens stat has everything in one package and therefore doesn't need connection B.



Next step! If I confirm that it's 230v switching as you mentioned above, then I need to wire it in. I'll put a L and N to the Seimens box for power. I then have to connect it somehow to, presumably, A and C to create the switch. The Siemens video confuses me a bit there. There is a link between L and Lx (as shown at 3.39 in the video). It then needs a "single core cable from L1 [on the Siemens unit] to the device." Where does this go to on the device? A or C? I assume it is whichever is the neutral out of A and C. In which case A (black wire) rather than C (red wire). In which case, how does it work with nothing going to the other wire (C). Perhaps the red wire is a permanent live from the board and the Siemens unit provides it's own permanent live from the L/Lx bridge.

https://www.youtube.com/watch?v=O0pTT3qSejc

It's all starting to make more sense now (or rather match what I initially thought before I got other advice) - thanks for helping guide me through it, much appreciated.
Post edited at 16:36
gethin_allen on 04 Oct 2017
In reply to NottsRich:

I'm also a bit confused as to what the patch between the Live and LX is, I think it's if the boiler requires a supply rather than just a switched connection, I'd check that the thermostat is switching (opening and closing the circuit between) L1 and Lx with just the L and N connected to the mains, and after checkijng what we said above, connect Lx to M5 C, and L1 to M5. This is similar to how my RF thermostat is connected.
Lusk - on 04 Oct 2017
In reply to NottsRich:

Having looked at this myself, all you need to do is connect M5-A to L1 & M5-C to Lx. (or the other way round, doesn't matter) as per fig 39.
What voltage A or C is at irrelevant, the receiver is cable of switching up to 230V .
If you want test for voltage at A and C, put one probe on your nearest Neutral and test A an C with the other probe.
Bear in mind it maybe DC, depends on what is being switched.
gethin_allen on 04 Oct 2017
In reply to Lusk:

Glad someone else agrees with me.
Lusk - on 04 Oct 2017
In reply to gethin_allen:

Hehe, sorry if I was repeating what you've already said, I didn't read all the above.
Mind you, it's always good to get an affirming second opinion
gethin_allen on 04 Oct 2017
In reply to Lusk:

Nothing to be sorry about, I'm just pleased that for once I may not be talking crap.
Lusk - on 04 Oct 2017
In reply to gethin_allen:

Ah, but that's an assumption that I'm not either!
NottsRich on 04 Oct 2017
In reply to gethin_allen:

> I'd check that the thermostat is switching (opening and closing the circuit between) L1 and Lx with just the L and N connected to the mains, and after checkijng what we said above, connect Lx to M5 C, and L1 to M5. This is similar to how my RF thermostat is connected.

In reply to Lusk:
> Having looked at this myself, all you need to do is connect M5-A to L1 & M5-C to Lx. (or the other way round, doesn't matter) as per fig 39.

You've both said the same thing, and it's what makes sense to me too. I'll go with this, but first I will check the voltage between A and C for peace of mind. Hopefully it's 24vdc and just needs a switch to close the circuit.

I assume that wiring it as you've both said, the stat acts simply as a switch. Worst case is that it doesn't work because it acutally needs a 230v supply to the switching circuit, in which case no damage done and I then need to wire it with the Lx/L bridge in place. If I try it round the other way first (wired for 230v) then worst case is I blow the PCB. If I understand how the stat works then your wiring suggestions are the safest way to go first.

I'll do some voltage testing tomorrow...
NottsRich on 06 Oct 2017

I tested the voltage in lots of places to confirm things, as was suggested above. The clock supply was 240v. The clock acted simply as a switch (open/close, no voltage across the switching wires in either position). Measuring the switching leads going to the clock (M5-A and M5-C) from the PCB showed these were 240v, not 24vdc or 0v. I checked L1/Lx on the Siemens receiver as well and that was just a switch too. Based on that, and your advice above, I was happy to wire it in as you both suggested. Bang! Nah, only joking - worked a charm. So thank you both very much, I've learned something along the way, been able to check out ideas with other people, and saved a bit of money too. Thanks!
Lusk - on 06 Oct 2017
In reply to NottsRich:

Bastard! I saw 'Bang!' and my heart stopped for second!

Anyway, result, happy days.
NottsRich on 06 Oct 2017
In reply to Lusk:

Haha, my heart was going when I turn it all on as well! No bang though, just finally the ability to properly control my heating, learn something, and save a bit of money.
marsbar - on 07 Oct 2017
In reply to NottsRich:

Great news.

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