Replacing Timer for CH/Hot water

[Tri]

Novice user, please excuse obvious questions...
I've read in detail previous threads regarding the replacement of an old Switchmaster 300 with a Horstman C17~which is exactly what I want to do.
There is one (or 2, really) outstanding pieces of information I need before attempting the re~wiring.

There is much talk of an L-2 link needed for mains voltage applications. My first obvious question is ; what is this link ? Do I need it? How do I link L-2? I don't see anything in the existing wiring that looks like a link. (I'm sure these sound like a really dumb questions to anyone who knows what they're doing, but I'm just trying to learn!)

The boiler is an old Vaillant Combi VCW-Sine18 T3WFH (26kw)

The wires are two sets of Brown /Blue/ Green & Yellow.
The two earths are in the same earth terminal and the other wires are connected as follows;

N (blue) L (brown) 1 (brown wire) 4 (blue)

Can anyone tell me how I should wire the C17? Other posts on DIYnot had different initial wiring, I assume the C17 wiring would be different too....

Hope someone can help!

Thanks for your time.....

 

[stem]

Some boilers require a 230 V live supply directly from the programmer to operate, others have internal circuits that provide the control supply which may be a different voltage such as 24v.

If the 230 V is required then the link between L and terminal 2 in the programmer provides it. If not, then terminal 2 will get its control supply from the boiler. I believe that the latter is the case for Vaillant, but please check the wiring diagrams in your manual to be sure.

If so, then you need a mains supply to terminals L & N on the programmer to make it work (don't link L&2) and then terminals 2 & 4 will provide the switching for the boiler. (connecting possibly to terminals 3 & 4 on the boiler, but again check your manual)

 

[Taylortwocities]

When you buy your C17 it will include a wiring chart. this will tell you exactly what cables on your old SM300 go where on the C17.

Do not worry about anything else, do not put any extra links in, just follow the chart - wire for wire - and make sure you select pumped or gravity system and the job's done.

EDIT The wiring chart is here
http://www.horstmann.co.uk/downloads/electronicdocuments/central-heating/wiringguide.pdf

Please note on the chart that the recommended programmer for the SM300 is
425 Coronet or CentaurPlus C11 or ChannelPlus H11XL

 

[Tri]

Thanks for your reply, I'm beginning to understand a little more of what is going on!

It sounds as if I'd be able to SEE if there is a link from L - 2 in the present wiring? Am I right in thinking that?
If so, nothing is present, so does that not imply that the boiler won't need it and has it taken care of internally.....?

If true does that mean I should wire it as you said; N L 2 4?

Sorry for the thousand more questions, but if such a link is NOT visible, how can I find out if there is one there?

Good idea to look in the boiler manual, but unfortunately, never had it (boiler came with the house) and can't find it online ~ there are some references to it in old posts, perhaps if anyone has a pdf of it they could send it to me? or drop box it if big...?
Much obliged if anyone could help with that! (Vaillant-sine 18 T3WF H 26kw)

Many thanks again for your reply, much appreciated.

 

[Tri]

Thanks also to Taylortwocities ~ didn't see your reply until now!
I'm afraid I'm a major novice, and have never even seen a wiring diagram before yesterday!
Getting clearer by the hour, but unfortunately I can't decipher the comparison charts you so kindly sent a link to. I found the exact comparison, but don't understand what the numbers actually in the columns are referring to...
This is what it says

Centaurplus C17

E N L 1 2 3 4

SM300 N,2 L 4 1


My SM300 was indeed wired N L 1 4
What is the chart telling me I should do?

I've had another good look at the wiring carts that came with the timer as you suggested and I'm inclined to wire it L, N exactly as before, then brown wire (being boiler live out) to 2 and neutral to 4. Does that sound sensible?

Important (if stupid) question ; what will happen if it's wrong?! hopefully the answer is simply nothing, but don't worry, I'm not going to attempt anything unless I am absolutely sure!

Big thanks for your help so far!

 

[Tri]

Sorry, chart above didn't come out with spacings, so has become nonsense!

with stars for gaps;

C17

L**N**1**2**3**4
L**N,2***4******1 SM300

L (SM300) is under L (C17)
N,2(SM300) is under N(C17)
4(SM300) is under 2(C17)
1(SM300) is under 4(C17)

Hope that's clearer...

 

[stem]

It sounds as if I'd be able to SEE if there is a link from L - 2 in the present wiring? Am I right in thinking that?
If so, nothing is present, so does that not imply that the boiler won't need it and has it taken care of internally.....?

Your existing Switchmaster 300 according to the wiring diagram I have, uses the following terminals. (earths should be connected to an earth terminal)

N = Neutral
L = Live
4 = Common
1 = On (Switched output to the boiler to call for heat)

If a link was required, it would be between the "L" and the "Common" In this case, terminals L & 4 and yes you would see it. If it's not there now, you won't need it with the Horstmann C17. (You will see from my first post that I suspected you wouldn't have one)

With the Horstmann C17 the wires would be

N = Neutral
L = Live
2 = Common
4 = On (switched output to the boiler to call for heat)

If a link is required, it would still be between the "L" and the "Common" In this case, terminals L & 2 but if you don't have the link now don't add it.

I've had another good look at the wiring carts that came with the timer as you suggested and I'm inclined to wire it L, N exactly as before, then brown wire (being boiler live out) to 2 and neutral to 4. Does that sound sensible?

Terminals 2 & 4 are certainly the ones to use. However, the wire you refer to above as going to terminal 4 won't be a Neutral. Quite often in these applications the blue wire is used for a switched supply.

If the SM300 is was working correctly, then connect the L & N accordingly
The wire that was in terminal 4 at the SM300 put to terminal 2 in the C17
The wire that was in terminal 1 at the SM300 put to terminal 4 in the C17

 

[Tri]

Fantastic!!!
All up and running. It's wired in and the heating is on, and switches off when I switch it off with the timer. That's more than good enough for now ~ I'll test all the programmings etc., another day.
I really appreciate your help, and your very specific and helpful final reply, stem~ just what I needed . Will click on thanks when I figure out how...
Same goes to taylortwocities ~ your reply was also very helpful and informative.

Cheers!

 

[ban-all-sheds]

This is what it says

Centaurplus C17

E N L 1 2 3 4

SM300 N,2 L 4 1

Try
[code:1]

Centaurplus C17

E N L 1 2 3 4

SM300 N,2 L 4 1[/code:1]

 

[stem]

stem~ just what I needed . Will click on thanks when I figure out how...

Glad it's all worked out OK. The thanks button is in the top right corner of each post (except those you post yourself of course)