The forth wire on a Ideal Logic 18kw Heat Only System Boiler
- Thread starter Ray1000
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if your boiler is wired as in your colour diagram with only L,N&E then is wired wrong, the wire in L should be in SL1 IN and a permanent live to the L terminal, it is important that this is sorted
Thank you Ian,
I shall double check if the white cable is in fact 3 core ... and report back.
Not being an Electrician or a Plumber I'm mystified about the "permanent" live.
When done properly does it mean that, even when the fused spur to the boiler is turned off there is 240v still going to the boiler - the type you could get electrocuted with?
I have another post in Electrical Dept asking about the terminals on the back of a Fused Spur if you could have a look.
Thank you for staying with me
Ray
I shall double check if the white cable is in fact 3 core ... and report back.
Not being an Electrician or a Plumber I'm mystified about the "permanent" live.
When done properly does it mean that, even when the fused spur to the boiler is turned off there is 240v still going to the boiler - the type you could get electrocuted with?
I have another post in Electrical Dept asking about the terminals on the back of a Fused Spur if you could have a look.
Thank you for staying with me
Ray
No, it just means that when the fused spur is switched on then the boiler is powered up, it's the switched live that activates the boiler to start it running.
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No, the fused spur incorporates a switch, which you open before working on anything.
Some boilers need a permanent live (ie permanent unless the fused spur is switched off!), some don't. Your first diagram shows that, and as it says Logic Heat H on it that is presumably what you have. The 2nd one has no permanent live, where does that diagram come from?
If you have a logic heat then the switched live comes from the 3 port valve, this brings the boiler and pump on, the permanent live is there for when the call for heat is satisfied the fan over-run can activate and cool the boiler and store settings, when the fused spur is switched off the permanent live and switched live are both isolated if wired correctly
Madrab & Fixit thank you for your help,
Ian, your point about the over-run has enlightened me ... In May 2019 we had a Ideal Logic 18kw System boiler fitted at our house - the coloured wiring diagram was made to ask a question on this forum when fitting a Nest thermostat in January 2022. The cable to the boiler is three core - so as you said at 12:42 it is wired wrong.
Yesterday we had the same boiler fitted in my son's house - there was a mention of a "it needs a permanent live to the boiler" and it was coming directly from the fused spur.
I think it may be on the input side which is the reason I asked about the connections on a Volex FS on the electrical forum.
Without disconnecting the cables you can't see the markings on the back, someone suggested using a mirror, I went back down this afternoon to do just that.
After turning the stat down and seeing the 0.00 on the screen I found myself waiting maybe a minute for the the boiler to stop ... something I've never noticed at our house and of course, I can see why - now you have explained it.
I took a picture of the back of the FS through a mirror but you can't see any markings. I turned the MCB off and the extra wire that had been fitted was dead, according to my 40 year old Trolex Deadline Indicator, similarly it was live with the MCB on and the FS off.
Now it's been explained its not actually permanently live - the extra wire has probably been fitted on the input rather than the output where it would have been isolated when the Fused Spur switch was opened or turned off.
Coming back to mine ... with the identical boiler and the coloured wiring diagram. Is there anywhere on the Honeywell board where the "permanent live" can come from to activate the cooling down process?
The Fused Spur is downstairs in the hall above the skirting - the Heat Link and Nest are directly above it at head height and the Honeywell board and Boiler are in the loft - I can't simply run a cable from the outlet of the FS to the boiler SL1 IN.
How could you fit a live to SL1 IN without going through the main FS and still be within the rules?
Ray
Ian, your point about the over-run has enlightened me ... In May 2019 we had a Ideal Logic 18kw System boiler fitted at our house - the coloured wiring diagram was made to ask a question on this forum when fitting a Nest thermostat in January 2022. The cable to the boiler is three core - so as you said at 12:42 it is wired wrong.
Yesterday we had the same boiler fitted in my son's house - there was a mention of a "it needs a permanent live to the boiler" and it was coming directly from the fused spur.
I think it may be on the input side which is the reason I asked about the connections on a Volex FS on the electrical forum.
Without disconnecting the cables you can't see the markings on the back, someone suggested using a mirror, I went back down this afternoon to do just that.
After turning the stat down and seeing the 0.00 on the screen I found myself waiting maybe a minute for the the boiler to stop ... something I've never noticed at our house and of course, I can see why - now you have explained it.
I took a picture of the back of the FS through a mirror but you can't see any markings. I turned the MCB off and the extra wire that had been fitted was dead, according to my 40 year old Trolex Deadline Indicator, similarly it was live with the MCB on and the FS off.
Now it's been explained its not actually permanently live - the extra wire has probably been fitted on the input rather than the output where it would have been isolated when the Fused Spur switch was opened or turned off.
Coming back to mine ... with the identical boiler and the coloured wiring diagram. Is there anywhere on the Honeywell board where the "permanent live" can come from to activate the cooling down process?
The Fused Spur is downstairs in the hall above the skirting - the Heat Link and Nest are directly above it at head height and the Honeywell board and Boiler are in the loft - I can't simply run a cable from the outlet of the FS to the boiler SL1 IN.
How could you fit a live to SL1 IN without going through the main FS and still be within the rules?
Ray
Connect the current wire in L at the boiler to SL1 IN, then run a permanent live from the honeywell wiring centre to the boiler L
I had wrongly assumed the live connections at 5, 9 & 10 would have been turned off by the Heat Link/programmer before they could run the cooling fan.
Will any of these connections do the job or is it just number 5 ... or something else?
Ray
Will any of these connections do the job or is it just number 5 ... or something else?
Ray
what is this cable and where does it connect to ?
Permanent Live is permanent only when the fused spur (fused connection unit) is ON, and its enclosed fuse is intact.
Switched Live is that which demands the boiler to run, and this comes from the external (to the boiler) controls.
The Permanent live allows the boiler to run both the circulating pump and the flue fan after controls have removed the Switched Live, such as when the thermostat is satisfied, or the timer switches off. The pump 'over-run' helps raise boiler efficiency by removing sensible heat from the boiler's heat exchanger (amongst other functions), the fan over-run helps to cool other boiler parts.
The Permanent Live also allows the boiler display to give user information when the boiler is not demanded, and helps to reduce electrical stress on the low voltage power supply when compared to that in your 'diagram of colour'.
Switched Live is that which demands the boiler to run, and this comes from the external (to the boiler) controls.
The Permanent live allows the boiler to run both the circulating pump and the flue fan after controls have removed the Switched Live, such as when the thermostat is satisfied, or the timer switches off. The pump 'over-run' helps raise boiler efficiency by removing sensible heat from the boiler's heat exchanger (amongst other functions), the fan over-run helps to cool other boiler parts.
The Permanent Live also allows the boiler display to give user information when the boiler is not demanded, and helps to reduce electrical stress on the low voltage power supply when compared to that in your 'diagram of colour'.
Thank you for that, I appreciate the need to get the extra wire fitted - I just need to work out how.
I started with one job and finished up with two ... my boiler has been running for nearly 3 years without the over run facility.
I’ll ring the firm who installed it tomorrow.
Ian, the white cable goes to the boiler.
Ray
I started with one job and finished up with two ... my boiler has been running for nearly 3 years without the over run facility.
I’ll ring the firm who installed it tomorrow.
Ian, the white cable goes to the boiler.
Ray
no the grey flat cable that I have circled in red
Not on this boiler it doesnt, the pump is activated by the switched live and no pump over run
I beg to differ, but only slightly. The circulating pump is [edit: should be]wired directly from the boiler.
[edit 2: there is confusion in the title; a heat only boiler is not a system boiler, and vice-versa]
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