Wet UFH Plumbing & Wiring

[vala]

So I've drawn up this schematic for my S Plan wiring centre and I hope most of it is correct. I'm lost as to where the brown cable from the zone valve (which is to go between the buffer and the boiler) goes so hoping someones can advise. I did think 4, but can't work out what else should be there. I'm did think it should be a switch live but I have this in 10. So definitely lost there.

I've looked through the MI for the boiler and all I can make out is a T&E for power, but unsure what else is going from it to the wiring centre. I've put in a SL in my diagram as I can make that out, but unsure if there should be another. I'm starting the rip out for the bathroom and floorboards on the first floor this Friday so I'll be sure to see what other cables there are going to it.

Also I've got hold of the buffer stat instructions from Newark Cylinders and according to that its a 2 core cable (COM and 1, which I believe to be 'call for heat').

So here it is, if anyone can help then that would be much appreciated.

 

Hi all,

 

 

 

 

Edited August 25, 2021 by vala

[vala]

Also is it possible to not have a zone valve at all in this system? Even bearing in mind when there will be 2 manifolds?

[RHayes]

9 hours ago, vala said:

Also is it possible to not have a zone valve at all in this system? Even bearing in mind when there will be 2 manifolds?

Yes.  You don't need a zone valve in this system.  Zone valves are to stop the flow of water to a part of the heating system when the system pump or main circulator is running for another element of the heating system.

 

In your system you have basically substituted all the zone valves for pumps instead.  There is a pump that will circulate from boiler to buffer and nothing else.  There is then a pump that will circulate from buffer to ground floor manifold (nothing else) and a pump that will circualte from buffer to first floor manifold (nothing else).  Therefore as all pumps are only circulating one part of the system each and not affecting the other parts, this effectively negate the need for any zone valves.

[PeterW]

@vala that wiring won’t work and will go bang as you have connected live to neutral through the item marked ‘BS’. 
 

I am going to say I don’t think you should be doing this - this isn’t something you need to guess at, or ask an Internet forum for advice as none of us know how your boiler is wired etc and I cannot give 100% confidence that the wiring as you state is correct. 
 

I suggest you get an electrician or a plumber who understands UFH to do this for you. 

[RHayes]

On 26/08/2021 at 00:02, vala said:

Hi all,

 

 

 

 

Some amendments are required to this diagram as wiring it like this will mean the boiler will maintain a hot buffer tank over the summer.

 

I'll start with the BS (assumed to be buffer stat).  The brown wire to BS needs to be connected to the blue from the Wunda wiring centre that is currently wired in to 10.  Thererfore you need to use a separate terminal (4 for example) to connect these 2 together.   If you don't use the zone valve as mentioned in my earlier post then this is all you need to do.

 

If you are going to use the zone valve then the brown from the zone vavle will need to connect to the blue from the BS (buffer stat).  

 

The reason the above diagram is not correct is that you have the wiring centre, the buffer stat and the zone valve potentially all asking the boiler to fire, however only one item shoudl be connected to the boiler directly and everything else should switch in sequence up to that point.

 

Trust this helps.

[RHayes]

34 minutes ago, PeterW said:

@vala that wiring won’t work and will go bang as you have connected live to neutral through the item marked ‘BS’. 
 

Whilst the colour is blue this isn't neutral.  This is switched live as mentioned in Vala's earlier post (Brown goes to Com and blue goes from 1).  Strictly the blue shoudl be intalled with brown sleaving to indicate that is has 230v live on it.

[RHayes]

On that diagram:

1 is permanent live

2  is Neutral

3 is Earth

10 is switched live to the boiler (shoudl be from the zone valve orange only)

 

You also need switch lives for the following (which you can use any of the other spare terminals for.

Switch live from the Wunda wiring centre to the buffer stat

Switch live from the buffer stat to the zone valve (brown) or directly to the boiler (terminal 10) if you aren't using the zone valve.

[vala]

@RHayes Thank you so much for this! It now makes sense to me with regards to the switching sequence. Seeing it on the drawing has made it all make sense.

I'll definitely omit the zone valves now I'm understand how these come into play in other set ups. And yes the pump on the boiler will circulate to the buffer, then the Wilo pumps on the manifold can draw from the buffer and circulate around the zones calling for heat.

You are 100% correct with the blue from the buffer stat being a switched live. Reason I did it in blue was to mimic the colours in the cable I'll be using to make it easier for me to start making sense and seeing practically how it will all go together.. And yes indeed,  if its live I'll definitely be using brown sleeving, as I have had to do for all the 2 way lighting I've installed.

I have attached the amended wiring diagram to show the correction and omitted the zone valve. Also shaded brown over other lives for the sleeving. I believe this now to be correct?

Today whilst stripping out the bathroom, I came across the 5 core cable from the boiler which went into the Tado extension hub. So there's another cable connected which hasn't been allowed for on the drawing. I'll pull the control unit out from the boiler over the weekend, and see where this goes to. Hopefully can make sense of it and fit it into the S Plan wiring I've drawn up.

Edited August 27, 2021 by vala

[OldSpot]

I'm looking at a similar set up and just out of interest did you consider two stats on your buffer tank? (I think Peter W may have intimated this in his first reply on this thread, with the 1/3 & 2/3rds)

This may help to reduce the boiler cycling as my understanding is that an oil boiler is either on or off i.e they have very little modulation.

From my limited research I gather the hysteresis on a tank stat is around 8^oC but with a two stat setup you could increase this differential. For example, boiler ON @ 40^oC and OFF @ 65^oC.

This would then allow the boiler to run (or shut down) for longer since UFH runs on lower flow temps.

So if your UFH requires a 40^oC flow temp and the buffer is @ 50^oC, it can still be provided without the boiler firing. Whereas with a single stat (set @ 65) the boiler will probably have refired.

 

One of the calculators I have seen suggests that to increase the temperature of 100 litres by 8^oC, it will take a 20kW boiler around 3 minutes to do so.

 

 

Edited August 30, 2021 by OldSpot

[vala]

@OldSpot I'd definitely be interested in this! Anything to reduce unnecessary firing up of the boilers good with me.

Would these just be 2 standard stats?

And how would that now wire up into the S Plan wiring centre?

 

[RHayes]

On 27/08/2021 at 22:18, vala said:

Reason I did it in blue was to mimic the colours in the cable I'll be using to make it easier for me to start making sense and seeing practically how it will all go together..

I do just the same.

 

On 27/08/2021 at 22:18, vala said:

I believe this now to be correct?

Yep, looks good to me.

 

On 27/08/2021 at 22:18, vala said:

Today whilst stripping out the bathroom, I came across the 5 core cable from the boiler which went into the Tado extension hub.

I'm not sure what a Tado extension hub does.  From checking up a little I assume it is a wireless rerceiver for tado controls.  If that is the case and assuming you are taking out the Tado controls and puting in Wunda then this extension hub will no longer be needed.  I may be wrong here.

[RHayes]

@OldSpot Yes a good idea.

 

How has you thought this would wire up with the 2 buffer stats?  I am not sure your wider histeresis would work with just 2 standard stats and no other components. On way I can think of is to have a couple of relays connected in a way that would hold one on when you are heating inbetween the two stats, but you may have other ideas.

[OldSpot]

@RHayes @vala

 

Hi @RHayes,

 

Yes, that's correct you would need more than just the two stats to make this work!

You'd need to use a latching (or holding) relay circuit would work.

So say we set Stat 1 to 40^oC and the other - Stat 2 - is set at 65^oC. In addition I think you'd also need a high limit stat for safety.

 

The temperature scenarios are:

<40^oC & <65^oC => Boiler ON

>40^oC & <65^oC => Boiler either ON or OFF

>40^oC & >65^oC => Boiler OFF.

 

Stat 2 would be normally closed and a relay would latch "across" Stat 1 (normally open) to ensure the boiler remained in the correct state (either on or off).

This would be dependent on both the actual tank temperature and also on whether the temp was rising or falling.

 

 

 

Edited September 1, 2021 by OldSpot

[RHayes]

Just been looking in to latching relays, and as far as I know most of them are designed to run with a pulse input not a continuous voltage. It may be easier to use a couple of SPDT relays and wire them in such a way that it acts as a latching relay this way you don't have the issue of constant voltage on the coil of the latching relay. 

 

I can do a diagram on this tomorrow if it helps. 

[PeterW]

Most of the STP type digital thermostats have adjustable hysteresis - you can set them based on a 10° C gap so set at 50°C they would come on at 40°C and go off at 60°C

 

https://www.thermosensedirect.com/acatalog/stp_low_cost_programmable_digital_thermostat.html

[OldSpot]

I'm building up a test circuit (when i get 5 minutes!) so will report back when it's complete.

[vala]

@OldSpot I spoke to Thermosense after @PeterW mentioned them in a previous post about having 2 stats on the buffer. They've asked for details of the buffer and what it is to achieve and say they can put something together and fingers crossed will be getting back to me this week. I'll post up what they say when I hear back.

[OldSpot]

@vala ?

 

Great, I was going to do the same but will wait to see what they come back to you with.

 

[OldSpot]

Can't work out to edit my previous post so thanks to @PeterW for the steer.

[vala]

@OldSpot

 

So Thermosense got back to me today and have noted this is something they can do however they needed a bit of guidance as to which sensor would be most suitable.

They have recommended something from their PT100 range,

https://www.thermosense.co.uk/category/rtd_sensors_pt100_pt1000_prt.html

or their thermocouple range,

https://www.thermosense.co.uk/category/thermocouple_sensors.html

 

Can anyone help as to identify which sensor would be best for this application?

@PeterW is this something you've done before using components from Thermosense?

[dpmiller]

Anything will do, it's going into a thermopocket and there are no response or max temp considerations.

[vala]

@OldSpot  @RHayes

 

So Thermosense have got back in touch and recommend 2 mineral insulated thermocouple sensors and 2 programmable thermostat's.

They have sent me the instructions for the thermostats

STP321-STP322 Instruction Manual.pdf

Can anyone with better knowledge on this type of install advise on how this all wires up?

At present the call for heat from the UFH manifold is to the thermostat on the buffer however I'm struggling to make sense how this pair of cables now becomes 4 and all works together to allow the boiler to only fire when under a certain temperature and not exceed another.

 

Thanks

Edited September 10, 2021 by vala

[OldSpot]

@vala.

 

Haven't forgotten, still haven't had chance to make up my circuit!

[vala]

@OldSpot

 

No problem. Tbh I'm a bit confused with the Thermosense stuff as they noted I'd have to have a programmer for each of the sensors.

I was under the impression I'd have both sensors going into a programmer and from there the pair of cables going into the S Plan wiring centre...:but it seems this is not the case.

be interesting to see how you do yours. Definitely keep me informed.

Thanks

[dpmiller]

they're bog standard cheapo temperature controllers. How you configure them is up to you...