Wiring confusing of RWB2 timer

[fabgav]

Hi all, I wanted to replace my RWB2 with a horstmann s27r programmer.

I am reasonably clever when it come to diagrams but I can not figure this out at all!.

Currently on the RWB2 I have

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• fabgav
• 10 Oct 2013
• 1

On the back of the RWB2 it shows the internals like this

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• fabgav
• 10 Oct 2013
• 1

as per the direct replacement rwb29
http://w3.siemens.co.uk/buildingtec...-controls/documentation/Documents/rwb29_i.pdf

and the horstmann s27r shows the same set up

as per
http://www.horstmann.co.uk/downloads/ElectronicDocuments/Central-Heating/S21-I.pdf

So in my mind, it should jus tbe a straight swap?

But it does not turn anything on when installed.

I then read on and think I have a fully pumped y plan system and saw a post saying about a common problem with this deisgn that the CH can not be run on its own.
I always though the HW had to be on for CH to be on.

This sounds like a y plan system.
A fairly common design fault with this system is that in order for it to work in heating only an extra signal is required to drive the valve into its third position.
The extra wire from the programmer is require to do this from the HW off terminal on the programmer.

However this is not required if the water has heated up when the valve should go to the heating only position.
This is only true however if the cylinder stat has been wired correctly to give the hw satisfied signal(they sometimes are not).

The cw output from the timer has to be on however for this to work even though the valve should only be open on the heating side.


Read more: //www.diynot.com/forums/viewtopic.php?p=1277794#1277794#ixzz2hMRNxje2[/QUOTE]

So 2 question really.

1. What wires do I need to change to get the new programmer to do its job (if any?).
2. Can i have just CH running for an hour without having the boiler on to heat the water?
(I understand this will just drain the heat from HW tank)[/url]

 

[stem]

You are right about the two units having identical connections. So if you have swapped like for like it should work as before. Have you checked the connections haven't pulled loose, or that you haven't trapped the insulation rather than the conductor.

However, your first diagram is rather puzzling.

1. If it's a Y plan, there are a lot of components & wiring missing from it

2. Also the Pump or Valve. What does that mean? it's either one or the other and they are certainly not wired the same. A pump doesn't require two live connections as you have shown.

3. If you can't have the central heating on without the hot water, it's either not a Y plan or if it's been incorrectly wired.

Click here for a wiring diagram for a Y Plan showing it in central heating mode only.

When you say it doesn't turn on anything. Do the CH & HW lamps illuminate on the programmer?

 

[fabgav]

Hi,
I only think it is a y plan from some other post I have seen.

I have 3 port valve pump tank and boiler.

The cable labelled pump/valve I am not too sure where it goes yet, (i've not had chance to check)

I've never tried to CH on its own, because I had always been told you could not do it.

The new unit says its all on but I dont hear the boiler kick in or the pump start

 

[MANDATE]

You have a 3 port valve which indicates a 'Y' plan but you need a 2 channel programmer to control CH and HW separately.
The valve operates over 2 halves.
The programmer has 3 power outputs as follows.
(1) HW ON A wire from this terminal will lead to the cylinder stat.
The power will pass through the stat to light the boiler.
The valve will be in the rest position which is HW.
When HW is satisfied, the stat diverts the power to the satisfied terminal of the stat, but this has no effect due to valve position.
(2) CH ON A wire from this terminal will pass through the room stat and lead to the white wire of the valve. This will drive the motor forward but a micro switch cuts the power at mid position.
The options at this point depend what was selected and what was satisfied or not. The valve may be required to stay in mid position if both HW and CH was selected and have not yet been satisfied.
In this situation when HW becomes satisfied and ths cylinder stat diverts the power, it diverts it to the valves grey wire.
Now the grey wire takes over from where the white left off and drives the motor forward over the second half, this closes the HW port and also triggers another micro switch to allow power out from the valves orange wire to light the boiler.
Of course if HW was not selected then there would be nothing to divert at the cylinder stat so an alternative supply has to be introduced and this is where the 3rd supply comes from the programmer.
(3) HW OFF The HW switch in the programmer is 'two way' so either 'ON' is live or 'OFF' is live but never both.
A wire from the 'HW OFF' terminal leads to the grey of the valve which operates as said earlier.
Straight away it can be seen you have no HW OFF wire so it would never operate correctly eve if you had the correct programmer.

As it happens my own system is gravity HW and pumped CH and the same programmer as yours so I can't have CH without the boiler being on, and if the boiler is on then I have HW. Of course I can have HW without the CH.
Also like yours my HW OFF terminal has no wire connected cause there is no use for it.
Beside introducing a two channel programmer you may have to change the cylinder stat if you have one, because it requires a 'two way' if power is to be diverted to the grey wire.
Hope all this makes sense!

 

[fabgav]

Hi Mandate,

Yes that pretty much all makes sense...ish haha

My programmer is a 2 channel one I though but then I doubt I have the correct stat.

Would you be able to draw up your wiring diagram you have on your programmer hopefully I can see why mine does not work that way.

thanks

 

[MANDATE]

The wiring on my boiler programmer
Term 1 HW OFF. No wire connected.
( would be required in a 'Y' plan when HW is not selected, this would feed the grey wire of valve to move it to CH position and supply power out of the valves orange wire to operate boiler/pump,because no power going to cylinder stat from programmer)

Term 2 CH OFF. No wire connected.

Term 3 HW ON. (Note I have a oil boiler and no cylinder stat) Wire to control box (via a boiler stat)so live when timer is ON and boiler stat controls boiler temperature and cylinder temperature.

Term 4 CH ON. Wire 'live' when timer is on to 'room stat', then 'switched live' from 'room stat' to 'pump'

The programmer is set for gravity HW and pumped CH so can have HW only but not CH only.
(In fact the cams are worn slightly and each morning when they are both set to come on, the CH cam operates about a minute before the HW cam, so I do have CH only for a minute. It's of no value, it just pumps the cool boiler water round the system till the HW cam operates.)

 

[MANDATE]

Just had a look at the instructions for both programmers and I agree all the terminals are the same and should be straight swap, even though the system does not match up with any standard.
Did you use the new back plate or not.
If not, the new programmer spades may not be making contact.
Have you got the correct programmer settings, although its not clear what your system is? I think its supposed to be fully pumped 'Y' plan even though the wiring is inadequate.
Both HW and CH can be over ridden when either ON or OFF, just thing when its on' it might be in overide situation.

I've recently obtained a RWB29.
I've mounted the backplate on piece of MDF.
I've wired in 2 lamp circuits.
One for HW and one for CH
I wired in the mains 'live' and 'neutral'
Mounted the programmer after setting for gravity HW and pumped CH
Plug in and switch on.
Now I have tried everything, switching, timing. over riding off to on and on to off.
programming etc.
This way you can prove everything before you install

 

[fabgav]

Hi again Mandate, sorry for late reply had to put it on hold.

No I did not change the backplate.....so that's a route to look down.

Having looked again at my system I do not have a 3 port valve, only a 2 port valve.

Hot water go's up into the HW cylinder and at the top of the coil there is a t junction then about 4 inch of pipe then a 2 port valve and onto the rad's.

All I wanted from this programmer was to have HW on only in the morning and then both HW and CH in the evening. Perhaps this programmer is not suitable.

I need a weekend on it!

Thanks for you input thus far!

 

[stem]

The programmer is not the restricting item, the existing plumbing is.

With your current configuration the hot water must be 'on' (terminal 3 is live) to operate the boiler and the pump. When you require central heating, terminal 4 becomes live as well and opens the valve feeding water to the radiators.

With the current plumbing as you describe it, you cannot have the central heating 'on' without the hot water being 'on' at the same time.

However, you can have the hot water 'on', on it's own.

Based on the information you have provided, I would expect the wiring to be as shown below. In the absence of other details, I have assumed that:

1. The pump is wired directly to the programmer. However, this may not be the case. Some are integral with the boiler or controlled by the boiler via terminals provided for this purpose.

2. There isn't a room or cylinder thermostat fitted.

3. The boiler requires L (Live) N (Neutral) and SL (Switched Live) which are connected as shown.

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• stem
• 15 Oct 2013
• 1

 

[fabgav]

Hi Stem,

I was aware that I could not have CH on its own.

My initial problem is I have straight swapped the programmers and in theory it should work, but it isn't.

I've done a new drawing tonight, hope it helps and makes sense.

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• fabgav
• 17 Oct 2013
• 1

 

[fabgav]

So yes your drawing is correct.............which brings me full circle as to why the new programmer will not straight sawp.........unless as mandate says the old backplate is naff

 

[stem]

There are other possibilities.

By coincidence the boiler has failed just at the time of the swap
Your new programer is faulty
The fuse has blown
One of the original wires was not securely in place and changing the programmer has disturbed it, or damaged the backplate

As Mandate suggests, either fit the new backplate supplied with the new programmer and then see what happens, or put back the original RWB2

 

[MANDATE]

I would test the new programmer with its back plate before installing.Testing for continuity from L to term 3 and L to term 4.
I realize you may not be able to get the meter probes direct on to the terminals, but extending the terminals with short wires will overcome this.