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.
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Discuss No switched live to boiler? in the Boilers area at Plumbers Forums
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.
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!
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.
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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?
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?!)
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!
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.
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.
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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.
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.
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!).
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 ....
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 ....
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!
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.
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.
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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.??
Yes, that is the proposal.
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Hi Cheshire
The consensus seems to be that what you described earlier is the way to go.
ie get electrician to:
Replace present 3 core cable to boiler with 4 core to carry both a perm live, and a switched live from terminal 10
wire UFH valve grey wire to live
wire UFH valve orange wire also to term 10 (there may be a spare core to implement that?)
job done!
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I think I will rather continue to seek advice than do a bang test - very grateful for the hints and tips, which is exactly what helped me discover the two point of supply issue. It was not me who wired it up in the first place!
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Indeed, all of that, plus I believe replace power supply to UFH valve with power supply from wiring centre (solving the two supply source issue, I do think this needs to be done for safety), and use cable between UFH wring centre and S-Plan wiring centre to connect to boiler enable on the UFH wiring centre, wiring it into S-Plan like a thermostat for another zone.
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Regarding power supply: I noticed that switching the boiler feed off near the boiler does not switch off the power to the central heating and hot water programmer (which is in the kitchen). Clearly the programmer is connected as without a live signal from it nothing central heating and hot water would not work. If the programmer is still on when the boiler feed is disconnected, does this not mean that the wiring centre may still get a live feed?
I might be wrong here, but if not, I am starting to wonder how this was all signed off - which it was, I remember the electrician going round for almost a day with another electrician who certified it all.
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I had a look into all the wiring today, including inside the boiler. All as expected and supporting the solution above. However, this also confirmed that the power supply to the programmer is indeed made locally in the kitchen (same consumer circuit breaker, but not isolated by boiler switch). So a live feed could be sent even when boiler switch is off. Luckily I isolated the consumer unit circuit breaker at all times when investigating the system.
The cable running from programmer to S-Plan wiring centre is only three core plus earth. So if I wanted to supply power to the programmer from the S-Plan wiring centre as it should be done, I could not run a neutral wire. In this context, would it be acceptable to use the neutral from the local supply?
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the dreaded 'borrowed neutral'
before answering, I wondered what model the programmer Is, and how it is wired. If it just switches the wiring centre via 'volt free' contacts with the live coming from the wiring centre and returning via the appropriate core, there would not be a hazard in the way you describe.
before answering, I wondered what model the programmer Is, and how it is wired. If it just switches the wiring centre via 'volt free' contacts with the live coming from the wiring centre and returning via the appropriate core, there would not be a hazard in the way you describe.
It’s a bog standard one, mine is iflo but the Drayton ones look identical. Definitely not volts free...it is the live feed going through for CH and HW. I am puzzled how this could be wired up like this only two years ago. As I said, luckily I removed circuit breaker before looking at wiring and did not touch anything before building up a through understanding, but the wiring centre could definitely be receiving a live feed from programmer even when boiler switch is off!
Similar plumbing topics
thanks....
yes, so my diagram and wording is...
Great summary and well done for getting it...
Thanks for the input on this, much...
