Drayton LP711 Backplate wiring for Combi boiler

Discussion in 'Plumbing and Central Heating' started by Navel Gaze, 15 Dec 2021.

  1. Navel Gaze

    Navel Gaze

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    Hi Community,
    I hope you can help with this one..? My Ideal Isar HE24 recently failed. Hot water, but no heating. Home insurance sent a man - he said the LP711 timeswitch was at fault and did a temporary fix as an override. So now, when the boiler is switched on the central heating is on continuously regardless of thermostat setting. hot water is delivered on demand. I bought a new LP711 timeswitch as a replacement part. When I look at the backplate - image uploaded below - there are two wires connected. A black wire (LHS of the image) from the cable going in to the boiler, and the blue wire (right hand side of image) taped off with insulation tape.
    What I don't know is how the engineer did the override. I have contacted him but he hasn't responded. I assume the override is at the backplate (as opposed to inside the boiler - I don't think that would make sense??). Would anyone like to suggest if the black and blue connected cables is the override, and if so, which slot they should go into. As I think you might expect, positions 1 and 2 are HW/CH off, and 3-4 are HW/CH on. I presume one of the other two cables in the trunking comes from the thermostat (wall mounted dial thermostat in hall) but I couldn't tell you which one. Any advice gratefully received. LP711.jpg
     
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  3. oilhead

    oilhead

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    You need to identify the wiring to your thermostat. The Brown wire from No 1 must be feeding your boiler, and I would think the black and blue are your room stat which is now disconnected. Had I done the temp fix, I would have left the room stat still in commission. In normal operation, there would only be a link to 1 from live and 3 would feed your room stat. The return from your room sta would be connected to your boiler switched live.
     
  4. ericmark

    ericmark

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    There is a single and duel channel upload_2021-12-15_19-34-6.png the LP711 is suppose to be the single channel. So the wiring looks correct. Wonder if by-passed thermostat not programmer?
     
  5. ianmcd

    ianmcd

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    Remove the link between L&1
     
  6. Navel Gaze

    Navel Gaze

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    Hi All,
    Thanks for taking the time to look at this one and adding your comments. I have done a little more digging. So I have removed the trunking and looked inside the 3A fuse box to help identify the cables. I have labelled these in the picture, and from left to right is what I believe to be the boiler cable in, the mains power and the thermostat cable. I now think this is the original wiring to the backplate, and that the gas engineer didn't touch this. I partly think that because I peeled back the black insulation tape around the connector and it was dry - if it was only a few days old it should still be tacky. Also, looking at wiring fit, I think the black wire going off to the boiler (the one that looks to be connected to the blue stat wire) - this black wire will only reach to position 3 on the backplate.
    Further, when the engineer was looking under the boiler, I heard him on the phone to a colleague talking about L1 and L2. In the Isar boiler manual these terminals in the boiler seem to relate to external electrical controls. So I now think the engineer has actually done something to the wiring inside the boiler as a temp fix override. I will take off the boiler plates and have a look, and report back here on findings.
    Thanks again
    lp711 v2.jpg
     
  7. oilhead

    oilhead

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    Without seeing the boiler connections, I cannot offer any other suggestion. I'm confused by the brown wires to L and 1. 3 feeds the room stat and the switch from the stat would return on the black and go to the boiler switched live. 230 volt would be supplied to the common pole of the timer switch by the red link from L to 1. It is possible that originally this link provides the power from 1 to L to provide a permanent live to your boiler as well as power the room stat.
     
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  9. CBW

    CBW

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    That’s how I follow it tracing the cables/wires from it being labelled.
     
  10. stem

    stem

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    That all looks fine to me once you consider that terminals L and 1 are just used as a common connection for all permanent lives. I was going to post that after looking at the first picture, but one thing stopped me, and made me decide to await the OP's reply to the request from @oilhead for more info. The thing that stopped me was....

    ....that I couldn't see an earth provided in what I thought was, and has now been identified by the OP as the 'power' supply cable :eek:. The only earths seem to be in the cables to the thermostat and boiler! Unless it's there and I need to go to Specsavers!

    So, my thought is that probably the "home insurance man" who bypassed it may have added a link between the permanent live and switched live at the boiler end.

    But I would want to get that earth checked, unless there's another earth connection somewhere, the boiler might not be earthed.
     
  11. Navel Gaze

    Navel Gaze

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    You are absolutely right Stem. There are 3 earths - at first, when I was stood right in front of it I only saw 2 - but the third earth from the mains power cable cunningly runs up behind other wires and then exactly parallel with the boiler earth wire, so nothing too shocking there... ;). I will take a look inside the boiler gubbins over the weekend when the day job isn't interfering and I will give you all an update and more pics then on how the wiring is configured. Thanks for the feedback.
     
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  12. Navel Gaze

    Navel Gaze

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    Hi All,
    So I have now been able to get at the wiring inside the boiler. A few pictures below to hopefully help. So, on the terminal connection, from left to right is L1, L2, earth, N and L3. What appears to have been done as a temporary override to keep the heating on constantly and override the stat is to disconnect the black wire (I think we established that this is the live connected to the N of the stat in the pics above). And then, a loop has been put in between L1 and L2 on the connector at the boiler end. The earth sleeve used on this loop looks clean and new, so I assume that is what has happened. Looking at the wiring diagram in the Isar Ideal manual, I am thinking that my boiler should be wired up as in figure C - So that means, the loop in the earth sleeve between L1 and L2 should be taken out, and the black wire coming in to the boiler from the timeswitch should go in position L2. Does that make sense and would any agree/disagree with my assumptions?? As always, thanks for listening and taking the time to reply.
    Terminal 1.jpg terminal 2.jpg wiring diag.jpg
     
  13. stem

    stem

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    Sounds good to me, the other other end of the black wire in the boiler cable now goes to L2, after the link between L1 & L2 has been removed.

    It's not good that the 'repair man' has just left the black wire left loose and uninsulated at the boiler, whilst the other end was still connected.
     
  14. Navel Gaze

    Navel Gaze

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    Thanks Stem. There were a few other things about the 'repair man' that left me feeling slightly uneasy that I haven't mentioned. I imagine the home insurance provider has chosen that plumbing/heating company because they are cheapest, and it did show.
     
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