No switched live to boiler?

[CheshireH]

Hi

for a few reasons (problem with hot water, possible smart heating installation), I familiarised myself with my heating system and wiring. Looks like a standard S-Plan with magnetic valves for hot water, central heating and UFH. Valves are controlled by normal standard backplate programmer, thermostat on unvented hot water cylinder, and a John Guest wiring centre for the UFH. However, the boiler (two year old Intergas system boiler) is only connected with a three core cable to permanent power supply - 1,2,3 in wiring box. There is no switched live wire from where the valve orange wires are connected (10). I googled forever but I cannot explain why the boiler starts up when a valve opens ( which it does - small delay in firing up and closing down), without receiving a switched live signal. It works, but since I am considering a smart installation, I need to know why...

Unfortunately, the hot water valve does not open automatically and needs to be opened manually. Possibly a faulty valve, as I checked the wiring. Or a faulty thermostat on the cylinder. Is it dangerous to keep the valve in manual open mode until fixed?

Thanks, Henrik

 

[Aquarius]

Which Intergas model is it? Do you have a Honeywell thermostat?

 

[CheshireH]

Intergas Compact HRE 40 SB. I do not have a thermostat for CH - I have a standard two channel programmer that switches CH and HW on and off. HW has a thermostat of course (and I fixed the issue I mentioned with hot water, it was wrong wiring on the thermostat). What I do not understand is why there is no switches live to the boiler from the wiring centre. The boiler does come on when a valve opens, I would just like to understand why...before I make changes for my smart heating project!

 

[Basher]

I don't understand either!
I'm not suggesting you to go into the boiler (strictly GasSafe territory), but if you've looked at its wiring tray underneath, is there a wire in pin1 of connector X2, and if so where does it go? That's supposed to be switched live.

 

[snowhead]

If the Boiler fires when the Valve opens then the valve has control of the boiler.
If there is only a single Live (and Neutral and Earth), then the Valve must be switching that and it must be linked within the boiler.

 

[Basher]

If the Boiler fires when the Valve opens then the valve has control of the boiler.
If there is only a single Live (and Neutral and Earth), then the Valve must be switching that and it must be linked within the boiler.

Which presumably means there is no fan overrun or pump overrun - is that not a bad thing?

 

[CheshireH]

I don't understand either!
I'm not suggesting you to go into the boiler (strictly GasSafe territory), but if you've looked at its wiring tray underneath, is there a wire in pin1 of connector X2, and if so where does it go? That's supposed to be switched live.

Definitely not wire going into boiler, other than power supply (brown, neutral, earth), which is connects directly to mains supply!

 

[EvilDrPorkChop]

Which presumably means there is no fan overrun or pump overrun - is that not a bad thing?

Won't do the boiler much good.

Sounds like it hasn't been wired up quite right. When there's nothing switched on, HW or CH or UFH is there any lights on the boiler?

 

[CheshireH]

Won't do the boiler much good.

Sounds like it hasn't been wired up quite right. When there's nothing switched on, HW or CH or UFH is there any lights on the boiler?

Yes the boiler is in stand-by when all valves are switched off. To be honest, it does exactly what it is supposed to do, it kicks in a bit after the valves open and I believe it also runs a bit longer when they close. But there is definitely no electrical connection - in fact the UFH valve is connected directly to the UFH wiring centre (which has no connection to the boiler), it is not even linked into the S Plan wiring! And of course in the wiring centre, there is no switched live out from the terminal anyway where the orange wires from the valves connect to (no 10). It looks to me as if the opening of the valves create a flow (?) that starts up the boiler, perhaps there are sensors of some kind in the boiler! Unfortunately I know nothing about plumbing, but I understand electrics a bit, and there is only mains power to the boiler!
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Not a great picture but you can see the 3 core from the boiler kn the right, which goes straight across into 1,2,3 mains supply, and the orange cables from valves with no wire connected to them - where The switched out should be.

 

[John.g]

Maybe the boiler is just cutting in/out on its own stat, the zone valves opening and closing are simply speeding up the process by circulating water through it, it should also start/stop occasionally if the zone valves never open.

 

[Murdoch]

Are you sure the green and yellow cable isn’t the switched live .... seem it A LOT

 

[CheshireH]

No goes into earth connection in wiring centre..

 

[Murdoch]

so the boiler man couldn’t be bothered to run a new cable to the boiler with a SL?

 

[CheshireH]

so the boiler man couldn’t be bothered to run a new cable to the boiler with a SL?

Possibly. I don’t know. Just wondering why it is working now...
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I have a bit more information that will hopefully yield an explanation from someone!

Reading through the boiler instructions, I realised that the boiler never goes into 'Waiting Mode', it stays on '1 Boiler shutdown when require temperature reached'. So I assume that the boiler controller essentially shuts the boiler down when it reaches a set temperature. Closing the valve will probably lead to reaching the temperature limit.

What I do not understand is why, in this case, the boiler does not switch itself back on when its internal temperature is reducing, even if there is no demand for heat. Or perhaps it does do that for a few minutes, before it reaches temperature again - I just might not realise?

Any advice? I am puzzled why one would not just connect a simple four core cable with a switched live to control the boiler. The wiring centre is right next to the boiler, and the installation was done from scratch, involving four core cable in various places, so there ws no pre-existing three core that somebody could not be bothered to replace. It must have been done lie this intentionally. Does anybody understand why?

 

[John.g]

I think that's what is happening as I mentioned in my other post, if you monitor it after cut out it should be easy to catch it firing back up as normally the cut in temperature is SP-5C. (Cut out SP+5C)

 

[CheshireH]

I think that's what is happening as I mentioned in my other post, if you monitor it after cut out it should be easy to catch it firing back up as normally the cut in temperature is SP-5C. (Cut out SP+5C)

Thanks John, is there any logic to this set-up? Is it acceptable? Will it do damage to the boiler? The installer is no longer trading, but I have had a boiler inspection from somebody else since who did mention that he would have wired things differently, but otherwise did not raise a concern.

What is SP by the way?

 

[Basher]

Cheshire - in you original post you mention two S-plan valves and a UFH Valve.
In your wiring centre (Terminal 10) you have just two orange wires, presumably from the Heating and HW zone valves, but should there be a further wire to call for heat for the UFH?
Maybe the boiler was connected up with switched live common with permanant live (ie 'on all the time') so that UFH has heat available even when the S-plan is not calling for it?
or maybe it's plumbed in a way that doesn't require a UFH Only demand.

 

[John.g]

Thanks John, is there any logic to this set-up? Is it acceptable? Will it do damage to the boiler? The installer is no longer trading, but I have had a boiler inspection from somebody else since who did mention that he would have wired things differently, but otherwise did not raise a concern.

What is SP by the way?

IMO, no logic in the way its configured, it should be configured as the S plan suggests.
SP = Set Point.

 

[CheshireH]

Cheshire - in you original post you mention two S-plan valves and a UFH Valve.
In your wiring centre (Terminal 10) you have just two orange wires, presumably from the Heating and HW zone valves, but should there be a further wire to call for heat for the UFH?
Maybe the boiler was connected up with switched live common with permanant live (ie 'on all the time') so that UFH has heat available even when the S-plan is not calling for it?
or maybe it's plumbed in a way that doesn't require a UFH Only demand.

Basher, the UFH valve is connected directly to the UFH wiring centre (just live, neutral, earth - grey/orange not used but GR/OR terminals are connected together in UFH wiring centre). Just as with CH and HW, the boiler starts up when the valve opens, without an electrical signal (no switched live).

John, if there is no logic in the set-up, can I just connect a switched live from the terminal with the two orange wires to the X2 connector no 1? Can I then also make a link between the live wire of the UFH valve and the same terminal where the switched live would come from (no 10 in my setup, which already holds the orange wire of the other two valves), so that the UFH valve opening would also activate the boiler?
Does this connection of one single wire need a qualified installer?

 

[John.g]

I think using somebody qualified is the proper/best way to proceed.

 

[CheshireH]

Another piece of information: I indeed just 'caught' the boiler switching on for a few moments without any valve being open - it went back to status '1' in the matter of perhaps a couple of minutes, with some 'banging' in the pipes. This really feels like something undesirable, can it damage something?

I would greatly appreciate anybody commenting on the possibility of connecting the UFH valve in the way I suggested. There is also a 'boiler enable in/out' on the UFH wiring centre (not 230V), which is unused, but I would need to run a cable across the garage - the UFH controls are not close to the valves and boiler - which has just been plasterboarded for use as a gym...

 

[Basher]

Another piece of information: I indeed just 'caught' the boiler switching on for a few moments without any valve being open - it went back to status '1' in the matter of perhaps a couple of minutes, with some 'banging' in the pipes. This really feels like something undesirable, can it damage something?

I would greatly appreciate anybody commenting on the possibility of connecting the UFH valve in the way I suggested. There is also a 'boiler enable in/out' on the UFH wiring centre (not 230V), which is unused, but I would need to run a cable across the garage - the UFH controls are not close to the valves and boiler - which has just been plasterboarded for use as a gym...

This sounds like a job for a wireless link rather than a cable.
I think your added wire suggestion (If you mean hard-wired) would result in the S-plan valves actuating the UFH valve, ie a demand for HW would open the UFH valve. A relay can be used to isolate, but again a wireless link would overcome this issue.
Also if by any chance the UFH electrics is on a separate circuit from the boiler, there could be a further complication of 'borrowed neutral' which could trip rcb's/rcbo's. A wireless receiver that connects tag (10) to (L), with a transmitter, either a thermostat for the UFH, or the contacts you describe, might do it.
Maybe a bit of design work is required to map out a preferred Thermostat/sensor scheme etc.
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This sounds like a job for a wireless link rather than a cable.
I think your added wire suggestion (If you mean hard-wired) would result in the S-plan valves actuating the UFH valve, ie a demand for HW would open the UFH valve. A relay can be used to isolate, but again a wireless link would overcome this issue.
Also if by any chance the UFH electrics is on a separate circuit from the boiler, there could be a further complication of 'borrowed neutral' which could trip rcb's/rcbo's. A wireless receiver that connects tag (10) to (L), with a transmitter, either a thermostat for the UFH, or the contacts you describe, might do it.
Maybe a bit of design work is required to map out a preferred Thermostat/sensor scheme etc.

Suggestion instead of cable;

https://plumbbox.co.uk/product/mains-switch-rf-solution-alternative-to-cabling/

or

RF Solutions MAINSLINK Remote Control System,869.5MHz | RS

uk.rs-online.com

 

[CheshireH]

I think your added wire suggestion (If you mean hard-wired) would result in the S-plan valves actuating the UFH valve, ie a demand for HW would open the UFH valve. A relay can be used to isolate, but again a wireless link would overcome this issue.

Thinking about this...yes, it would put the orange wires to the other valves live, yes, but without the motor of the HW/CH valve running (i.e. being activated by the programmer and thermostat), would these valves really open? Perhaps I am missing something...

I have been looking around, and really the right way of doing this, I believe, would be to run the (not 230V) boiler enable cable to the boiler. John Guest calls this a 'Voltage Free' connection, what does this mean? Could this connection be made wirelessly?

 

[Murdoch]

OP you really need to get a decent heating / spark involved and make sure they understand what you are trying to achieve before they tamper with it

 

[Basher]

Thinking about this...yes, it would put the orange wires to the other valves live, yes, but without the motor of the HW/CH valve running (i.e. being activated by the programmer and thermostat), would these valves really open? Perhaps I am missing something...

I have been looking around, and really the right way of doing this, I believe, would be to run the (not 230V) boiler enable cable to the boiler. John Guest calls this a 'Voltage Free' connection, what does this mean? Could this connection be made wirelessly?

OK, sorry, I misunderstood what the UFH valve was. If it's the same sort of valve, generally speaking, as your S-plan valves, with microswitches operated by actuation, you are right - there's no 'back feed' issue, and your wire suggestion would work.

A 'voltage free' option is effectively a set of relay contacts, generally a single pole double throw 'switch', so you can choose to use the 'normally open' or 'normally closed' as you need. The relay contacts typically capable of switching mains, but wise to check.
Yes I think you could make a connection wirelessly, either from the volt free contacts switching a transmitter on, or from the orange wire if that can provide the necessary. Then a receiver by the wiring centre connecting (10) to (L)

 

[John.g]

Thinking about this...yes, it would put the orange wires to the other valves live, yes, but without the motor of the HW/CH valve running (i.e. being activated by the programmer and thermostat), would these valves really open? Perhaps I am missing something...

I have been looking around, and really the right way of doing this, I believe, would be to run the (not 230V) boiler enable cable to the boiler. John Guest calls this a 'Voltage Free' connection, what does this mean? Could this connection be made wirelessly?

Just for interest here is a very basic but clear picture of a S plan but without pump overrun, there are probably others around showing a UFH zone and pump overrun which would mean a permanent live to the boiler as well as the switched live from terminal 10 but not from terminal 10 to the circ pump as this is/will be switched by the boiler PCB in all cases.

 

[CheshireH]

OK, sorry, I misunderstood what the UFH valve was. If it's the same sort of valve, generally speaking, as your S-plan valves, with microswitches operated by actuation, you are right - there's no 'back feed' issue, and your wire suggestion would work.

Thanks for all the responses, I am almost there (and no worries, I will not open the boiler myself, but it will help, and hopefully make it cheaper, to be able to specify what is needed). While I also feel that the back feed may be no issue (as one orange would also 'back feed' a live onto the other one in a normal S-Plan setup), I am not fully sure - the live from the wiring centre to the UFH valve is on a different fused spur, would this create a short circuit when the CH or HW valve is open, and the microswitch gets a live from 'both sides'?
I feel that I should ignore what cabling I have right now and decide what is right. Everything is wired as in John's S-Plan diagram for the CH/HW, with the exception of course of the missing switched live connection to the boiler. This part will be easy to explain to boiler engineer.
The UFH wiring centre (see attached wiring diagram) has the voltage free 'boiler enable' connection, and all five connections (L,N,E,GR, OR) to the UFH valve. My last remaining question is - how do I connect the UFH wiring centre? Should the UFH valve get directly connected, with no link into the S-Plan wiring centre next to boiler (as it is now, although orange an grey are not used and are just linked in the wiring centre)? And does the boiler enable go directly to the boiler, perhaps into the x4 24V thermostat connections? Would the boiler then be switched on by either the UFH 'boiler enable', or the switched live from the standard S-Plan 'no 10'? Can these two connections co-exist?

 

[Basher]

Thanks for all the responses, I am almost there (and no worries, I will not open the boiler myself, but it will help, and hopefully make it cheaper, to be able to specify what is needed). While I also feel that the back feed may be no issue (as one orange would also 'back feed' a live onto the other one in a normal S-Plan setup), I am not fully sure - the live from the wiring centre to the UFH valve is on a different fused spur, would this create a short circuit when the CH or HW valve is open, and the microswitch gets a live from 'both sides'?
I feel that I should ignore what cabling I have right now and decide what is right. Everything is wired as in John's S-Plan diagram for the CH/HW, with the exception of course of the missing switched live connection to the boiler. This part will be easy to explain to boiler engineer.
The UFH wiring centre (see attached wiring diagram) has the voltage free 'boiler enable' connection, and all five connections (L,N,E,GR, OR) to the UFH valve. My last remaining question is - how do I connect the UFH wiring centre? Should the UFH valve get directly connected, with no link into the S-Plan wiring centre next to boiler (as it is now, although orange an grey are not used and are just linked in the wiring centre)? And does the boiler enable go directly to the boiler, perhaps into the x4 24V thermostat connections? Would the boiler then be switched on by either the UFH 'boiler enable', or the switched live from the standard S-Plan 'no 10'? Can these two connections co-exist?

Hi Cheshire
Just forget my comment about 'back feeding'. Doesn't happen with motorised valves with orange wires - irrelevant. Sorry to have confused things.
I have the same boiler, and am very pleased with It. We have a wireless link for the tank stat because we're in the same position as you with difficult to get a cable through. Thoroughly recommend a wireless option!
you've got options at the UFH end as to where the demand signal comes from, so just get help from a boiler experienced electrician to advise on the best way ahead. Evohome next!

 

[fixitflav]

Intergas Compact HRE 40 SB. I do not have a thermostat for CH - I have a standard two channel programmer that switches CH and HW on and off. HW has a thermostat of course (and I fixed the issue I mentioned with hot water, it was wrong wiring on the thermostat). What I do not understand is why there is no switches live to the boiler from the wiring centre. The boiler does come on when a valve opens, I would just like to understand why...before I make changes for my smart heating project!

Are you sure the wire to the boiler is permanently live, not just when firing called?
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Intergas Compact HRE 40 SB. I do not have a thermostat for CH - I have a standard two channel programmer that switches CH and HW on and off. HW has a thermostat of course (and I fixed the issue I mentioned with hot water, it was wrong wiring on the thermostat). What I do not understand is why there is no switches live to the boiler from the wiring centre. The boiler does come on when a valve opens, I would just like to understand why...before I make changes for my smart heating project!

Tried to edit earlier post but it wouldn't send. Apologies if this is already covered, I haven't waded through the whole thread.
You say it's wired straight from the mains, but have you checked at the boiler with a voltmeter? Or carefully, with a 240volt light bulb if you don't have a meter.

 

[CheshireH]

Are you sure the wire to the boiler is permanently live, not just when firing called?
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Tried to edit earlier post but it wouldn't send. Apologies if this is already covered, I haven't waded through the whole thread.
You say it's wired straight from the mains, but have you checked at the boiler with a voltmeter? Or carefully, with a 240volt light bulb if you don't have a meter.

I have not opened the boiler, but the cable coming out from it (L,N,E) goes straight into the mains power supply. The boiler also never goes into waiting mode, it remains on, but switching into 'Boiler shutdown when required temperature reached' mode when all valves are closed. It sounds to me that the boiler switches into this mode when no more heat is allowed through the valves. Unfortunately, it also switches on for a short moment every once in a while if the valves remain closed - I assume this happens when the temperature drops again in the boiler. So far, nobody has said anything about whether this setting is acceptable (could it damage the boiler or create other issues), but most folks on the thread did not think that this was a desired set-up.
Frankly, speaking, all I woudl need to do, I think, to remedy this is connect a switched live wire from the no 10 connector (where orange valve cables end) in my S-Plan wiring into the boiler at x2 230V connector no 1. This would take five minutes to do, unfortunately I do not know whether there are any settings that I need to change at the boiler once a switched live has been added?
And I think I would have to take out the link between no 6 and no 7 on the x4 connector?

 

[John.g]

Are you referring to the photo in post#12?, I see 6&10 and 8&10 linked there, I also see 2 orange wires going to terminal 9?. If you have a Mmeter you can see very quickly if the orange wire(s) terminal has 230V when the zone valves are switched, also where is the boiler circ pump fed from?.

 

[Basher]

Are you referring to the photo in post#12?, I see 6&10 and 8&10 linked there, I also see 2 orange wires going to terminal 9?. If you have a Mmeter you can see very quickly if the orange wire(s) terminal has 230V when the zone valves are switched, also where is the boiler circ pump fed from?.

Hi John - I think there's a parallex effect in the photo and the orange wires are actually in 10, at least that's what I assumed throughout the thread!
So far I have become convinced the boiler is wired to permanent live and is on all the time!
Agreed it would be good to check volts on 10 (or is it 9?!)

 

[CheshireH]

Hi John - I think there's a parallex effect in the photo and the orange wires are actually in 10, at least that's what I assumed throughout the thread!
So far I have become convinced the boiler is wired to permanent live and is on all the time!
Agreed it would be good to check volts on 10 (or is it 9?!)

You are right Basher, the orange ones are on 10! And of course I could check whether there is voltage on 10 (I am just a bit reluctant to open an electric panel before switching off supply, I never usually do that...), although I am totally convinced that there is, following all the logic of a standard S-Plan. But the voltage on 10 is not taken anywhere, so I am now convinced that the solution would be to connect terminal 10 on my S-Plan wiring to the Switched Live terminal on my boiler (x2 connector no 1 on the Intergas Compact HRE). Question 1: Would you concur from what you can see?
I have also thought about how the UFH zone valve could be brought into play, as this valve is directly connected via L, N, E, only to the UFH wiring centre. If I connected the grey wire from this valve (currently unused) to terminal 1 permanent live (alongside the grey wires from the other two valves), and the orange wire (currently unused) to Terminal 10 (alongside the orange wires from the other two valves), I believe that the microswitch in the UFH zone valve would close when the valve is activated, and provide a live to the no 10 terminal, just as the other two valves do via their orange wires. Question 2: Does this make sense to you?
I have read the boiler instructions, and connecting one wire from the wiring centre to one connector in the boiler is a 5 minute job. No other wires would have to be changed. I may have to take out the link between 6 and 7 on the x4 connector, which I believe makes the boiler think that it needs to be permanently on. I would obviously do this with the power supply turned off. This should then result in the boiler coming on and off when valves are opening or closing. Question 3: Does this make sense, and would this require any other setting change to the boiler?
Thanks for all the help, it is all clear in my head now, would just appreciate some additional views!

 

[Basher]

Speaking as a non-expert (but as an engineer, kept warm by an Intergas HRE 40SB)
1) Yes
2) Yes (but only if the UFH wiring centre is on the same Consumer Unit breaker)
3) Yes, No

there is a regs/safety issue that the boiler system should be isolated by a single switch (eg fcu), and so 'injecting' live mains from another part of the house, that has separate isolation, would be a safety problem. Might be acceptable as a one-off experiment to prove it works, but not a permanent solution. That's why i suggested a wireless link to close the circuit in the boiler wiring centre, making isolation of the supply legit.

 

[CheshireH]

Speaking as a non-expert (but as an engineer, kept warm by an Intergas 40SB)
1) Yes
2) Yes (but only if the UFH is on the same Consumer Unit breaker)
3) Yes, No

Basher, thanks, and you touched on the one thing that I also just thought about. The earth, live and neutral to the UFH zone valve is provided from the UFH wiring centre, which does not have the same power supply feed as the S-Plan wiring. The are both in the garage, but have different isolation switches. I switch off one circuit breaker in the kitchen to remove power from all of the garage (and indeed other parts of the house). Is that what is meant by being on one Consumer Unit breaker?

 

[Basher]

Basher, thanks, and you touched on the one thing that I also just thought about. The earth, live and neutral to the UFH zone valve is provided from the UFH wiring centre, which does not have the same power supply feed as the S-Plan wiring. The are both in the garage, but have different isolation switches. I switch off one circuit breaker in the kitchen to remove power from all of the garage (and indeed other parts of the house). Is that what is meant by being on one Consumer Unit breaker?

I've added a little to my previous post since you probably first read it.
The major issue is regulatory, which i tried to cover in that additional note.

the other is practical, and basically about taking current from one house circuit (eg garage) and returning it through another (eg kitchen), which can cause residual current devices to trip. And it's not supposed to be done!

Could you just clarify, if you switch off Mains power to the garage in the main 'fusebox', does that turn off the boiler as well? Ie that would mean they are on separate circuits.

 

[CheshireH]

the other is practical, and basically about taking current from one house circuit (eg garage) and returning it through another (eg kitchen), which can cause residual current devices to trip. And it's not supposed to be done!

Could you just clarify, if you switch off Mains power to the garage in the main 'fusebox', does that turn off the boiler as well? Ie that would mean they are on separate circuits.

there is a regs/safety issue that the boiler system should be isolated by a single switch (eg fcu), and so 'injecting' live mains from another part of the house, that has separate isolation, would be a safety problem. Might be acceptable as a one-off experiment to prove it works, but not a permanent solution. That's why i suggested a wireless link to close the circuit in the boiler wiring centre, making isolation of the supply legit.

If I trigger the first consumer unit circuit breaker in the main fusebox (which just happens to be n the kitchen), all power to our extension, the garage and also the UFH, the boiler, and the CH/HW programmer. goes off.

The switch for the boiler would still shut everything down, as the live feed going into the valve microswitch (grey wire) would be taken from the wiring centre. Switch-off - no supply to the grey cable - no power to the boiler - or am I misunderstanding something. The only think that would still happen (but that is the same today!) is that the UFH valve can open, as it is supplied from the UFH wiring centre.

Which rings me to another idea: Why do I not wire the UFH valve into the S-Plan just as the other two, feeding from the same power supply as everything else, and use the cable to the UFH wiring centre as the boiler enable (i.e. thermostat) cable? That would sound straightforward and 'cleaner', except that the John Guest UFH wiring diagram (attached above) says not to wire the boiler enable connection into the wiring centre...I had no idea why not, it would work just like the hot water stat...Any idea?

 

[Basher]

If I trigger the first consumer unit circuit breaker in the main fusebox (which just happens to be n the kitchen), all power to our extension, the garage and also the UFH, the boiler, and the CH/HW programmer. goes off.

The switch for the boiler would still shut everything down, as the live feed going into the valve microswitch (grey wire) would be taken from the wiring centre. Switch-off - no supply to the grey cable - no power to the boiler - or am I misunderstanding something. The only think that would still happen (but that is the same today!) is that the UFH valve can open, as it is supplied from the UFH wiring centre.

Which rings me to another idea: Why do I not wire the UFH valve into the S-Plan just as the other two, feeding from the same power supply as everything else, and use the cable to the UFH wiring centre as the boiler enable (i.e. thermostat) cable? That would sound straightforward and 'cleaner', except that the John Guest UFH wiring diagram (attached above) says not to wire the boiler enable connection into the wiring centre...I had no idea why not, it would work just like the hot water stat...Any idea?

Thanks.
Clarity - it's all on the same breaker in the fusebox, good.
So a reasonable idea to take a (L) from the boiler wiring centre to the UFH valve microswitch, and from the valve orange Back to join terminal (10). Worth a try!

The safety issue remains in that someone working on the UFH wiring centre might turn off the local switch (fcu?) to work on it, and unexpectedly find live wires (from the boiler). I'll be told off for suggesting that might be mitigated by labelling.

I would personally favour this mains option, rather than delving into the JG UFH box, otherwise I suggest involving a heating professional for advice.

 

[CheshireH]

The safety issue remains in that someone working on the UFH wiring centre might turn off the local switch (fcu?) to work on it, and unexpectedly find live wires (from the boiler). I'll be told off for suggesting that might be mitigated by labelling.

Thanks Basher, why would there still be a live wire from the boiler? The only live wire not switched off by the boiler switch would be the feed to the UFH zone valve, but the microswitch (grey to orange) would no longer close as grey would not receive a live feed any more, and thus no orange would be live. Again, I may be missing something?
But to be fair, you have a very valid point, as there is a safety concern around the wire to the UFH valve, which could be live even when the boiler switch is triggered. This problem is already in place today, of course, and made worse by the fact that the connection between the UFH valve and the UFH wiring centre is made through the terminals 11 and 12 in the S-Plan wiring centre!!!

This may be a reason to actually pursue the thought of wiring the valve fully into the S-Plan, and only connect to the UFH wiring centre via the 'volt free' boiler enable link. So if no current exists in the S-Plan wiring centre, no current will ever flow back from the UFH wiring centre. I have contacted John Guest for advice on this, but I am more and more certain that this is the right way of doing it. It would be easily executed, as I could use the existing cable to the UFH valve for the boiler enable link, and connect the UFH valve locally to the S-Plan wiring which is right next to the valve!).

 

[Murdoch]

OP .... you seem to have made up your mind what you are going to do so crack on with the bang test

AND you shouldn’t have 2 points of supply to your central heating system - it tends to irritate the guys who service them as they don’t like getting shocks ....

 

[Basher]

Thanks Basher, why would there still be a live wire from the boiler? The only live wire not switched off by the boiler switch would be the feed to the UFH zone valve, but the microswitch (grey to orange) would no longer close as grey would not receive a live feed any more, and thus no orange would be live. Again, I may be missing something?
But to be fair, you have a very valid point, as there is a safety concern around the wire to the UFH valve, which could be live even when the boiler switch is triggered. This problem is already in place today, of course, and made worse by the fact that the connection between the UFH valve and the UFH wiring centre is made through the terminals 11 and 12 in the S-Plan wiring centre!!!

This may be a reason to actually pursue the thought of wiring the valve fully into the S-Plan, and only connect to the UFH wiring centre via the 'volt free' boiler enable link. So if no current exists in the S-Plan wiring centre, no current will ever flow back from the UFH wiring centre. I have contacted John Guest for advice on this, but I am more and more certain that this is the right way of doing it. It would be easily executed, as I could use the existing cable to the UFH valve for the boiler enable link, and connect the UFH valve locally to the S-Plan wiring which is right next to the valve!).

Hi Cheshire
I didn't get that there is already a direct connection between the UFH wiring centre and the boiler wiring centre!
The scenario I was concerned about was when boiler/kitchen circuitry left on, garage UFH locally isolated for maintenance. But no point in debating as they are already interconnected wiring centres!

Sorry I may be misunderstanding your suggestion. If you implement the 'volt free' signalling from UFH to boiler but still have orange wires terminal (10) to boiler switched live, the UFH can surely only come on when one of the others demands heat as well, and when the UFH goes off, it all goes off!
I hope I'm wrong!

 

[Brambles]

From your initial description, the most likely scenario is that your boiler has been wired without any external control switching into X2 (volt free) or X3 (240v) Consequently the boiler is just operating 24/7 on the flow temperature thermostat. A rather inefficient mode of operation.

The motorised valves have presumably then been wired independently, to allow boiler output to flow into the heating system.

The easiest way to check this is to ask your installer to ckeck or confirm if the boiler X2 and X3 terminals are both bridged across the input pins.

Thereafter, it can be conventionally (S Plan?) rewired to respond to room thermostat inputs.

Alternatively to test this therory, turn all room thermostats to their lowest setting and the boiler thermostat to its highest setting. Even with no hot water demand and no heating demand, as the boiler flow temperature cools, the boiler will fire.

 

[John.g]

Hi Cheshire
I didn't get that there is already a direct connection between the UFH wiring centre and the boiler wiring centre!
The scenario I was concerned about was when boiler/kitchen circuitry left on, garage UFH locally isolated for maintenance. But no point in debating as they are already interconnected wiring centres!

Sorry I may be misunderstanding your suggestion. If you implement the 'volt free' signalling from UFH to boiler but still have orange wires terminal (10) to boiler switched live, the UFH can surely only come on when one of the others demands heat as well, and when the UFH goes off, it all goes off!
I hope I'm wrong!

The signal from the UFH would have to operate a relay with one set of contacts wired like the zone valve "end switch" ie a grey permanent live to one side and a yellow (switched) from the other side to terminal 10, that way all three zones are independent.??

 

[Basher]

Hi John.g
As I understand it, the grey and orange wires on the UFH 2-port valve are currently unused, so could be connected directly to L and terminal 10. Simples!

 

[John.g]

Grand so, that's the way to do it alright.

Does the boiler still need a permanent live though as well as the (proposed) switched live, most boilers do for overrun etc.