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Wiring when replacing DPST heating switch with Boost button

Discussion in 'Electrics UK' started by terraling, 14 Oct 2019.

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  1. terraling

    terraling

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    I have an existing simply DPST switch that operates the heating, firing up the oil boiler and also turning on the pumps to circulate the water in the rads.

    I'm trying to swap it out for Boost-button timer switch.

    The existing switch, aside from earth, has L1 & N1 and L2 & N2 connections.

    As you can see in the image, the L1 and N1 connections are both fed by the same brown wire, which is the only live wire. The L2 and N2 connections have grey and black wire attached.

    My Boost button switch has L(IN) and L(OUT) and N(IN) and N(OUT) connectors. I'm not sure which to connect where.

    The things I tried either don't work, or seem to work (the boost button starts up the boiler alright, but the circulation pumps run continuously).

    Anyone able to clarify which to connect?
     

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    Last edited: 15 Oct 2019
  2. EFLImpudence

    EFLImpudence

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    Are you sure? That would be very odd.

    OK. Whatever arrangement is in place, you should retain the switch and fit the boost somewhere else - under the switch? - so that the existing switch isolates all of the heating.

    You need to determine where they go and what they do.

    So - the same - except you don't have the Neutral connected to it.
    Do you have a neutral in the back box.

    That's because the boost presumably doesn't switch the Neutral which you are using for a Line(live) conductor.
    It would seem to verify what you said about boiler and pump.
    Does the boost not require a Neutral to work?

    Put both the Grey and the Black in the left hand terminal (looking at the picture) , move the Line(live) to the left and do away with the link wire.
    Put the Neutrals in the Neutral terminals.

    Do you not have a timer or thermostat for the heating?


    I'm still not sure this is a satisfactory arrangement.
     
    Last edited: 14 Oct 2019
  3. SFK

    SFK

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    My presumption is that the all the wires are Live (ie there is no Neutral at this socket unless there are other wires you are not showing) and you currently have:

    L1 Brown (LiveIn)
    ...switch...
    L2 Grey (Switched Live out to Boiler)

    N1 Black (Switched Live out to Pumps)
    ...switch...
    N2 Brown (LiveIn)

    So on your new booster you want:

    L(IN) Brown (LiveIn)
    ...switch...
    L(OUT) Grey (Switched Live out to Boiler)

    N(IN) Brown (LiveIn)
    ...switch...
    N(OUT) Black (Switched Live out to Pumps)


    But as said this is a guess. And it seems a strange wiring. You need to test with a multimeter and not guess the connections.
     
    Last edited: 14 Oct 2019
  4. SFK

    SFK

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    Good point from EFL regarding your boost switch not being two switches, and only switching the side labeled 'Live'.

    If the N side of the Boost Switch is not actually a switch, but is an always connected link, then my wiring above will cause the effect you are seeing of the "the circulation pumps [to] run continuously".

    You would then be better off keeping the switch you have and having the Boost Switch switching the Brown Wire before this switch. But note that I think my "Timeguard" Boost switch also needs a Neutral to power up its lights and its electronic timer.
     
    Last edited: 14 Oct 2019
  5. EFLImpudence

    EFLImpudence

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    I have edited my post because I had the existing switch terminals the wrong way round, left and right.
     
  6. ericmark

    ericmark

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    I would guess it should have been a three position switch, off, domestic hot water, central heating.

    So a line in, one to the boiler, and one to pump, so boiler without pump did domestic hot water and with pump the central heating.

    However it does seem a bit basic, and one wonders why? And automating not very easy without a neutral.

    Personally if it was mine I would want a thermostat, but you really do need work out what is actually there.
     
  7. SUNRAY

    SUNRAY

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    This was a common arrangement with a thermostat before the live in (brown wire), there is often additional devices around the switch (possibly relating to hot water) hence the need for a DP switch. assuming there are other devices you will need a timer with 2 contacts or a DP relay controlled by the timer.
    If you are able to say there are no other control devices in use, CATEGORICALLY NOTHING ELSE! Then the black and grey can be connected together for a single contact, in which case brown to L(in), black and grey to L(out) and you will have to find a neutral for N(in).

    Apologies if this has been said already.
     
  8. terraling

    terraling

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    Thanks for the replies everyone, I'm going to read them closely tomorrow while looking again at the switch(es).

    There are actually two. It's a crude arrangement given how modern the house is (10 years).

    There is an oil boiler. There are two switches. One for the hot water, one for the heating.

    Turn on the hot water, it fires up the boiler and—I think—a pump that sends the water to the hot water tank.

    Turn on the heating switch it fires up the boiler and the pumps that circulate the water in the rads. There are a couple of thermostats around the house but I'm not sure how effective they are or where they are wired back to, but in terms of the overall control it's these two separate on-off switches.

    The intention was to replace the switches with booster/timer switches so that instead of turning on the hot water boiler only to forget about it and come back to it 3 hours later to turn it off I would just use the boost button to turn it on for 30 mins or an hour.

    Likewise the heating. I don't have enough confidence in the thermostats to leave the heating on and let it settle at the intended temperature.

    (I have had heating engineers round for certain things and invited them to charge me for a few hours to work out how everything is hooked up, but they've only ever been interested in fixing the specific thing they've been called out for, hence I'm doing it myself.)

    As for whether the other wires are also live, not according to the multimeter, but I'll double-check that tomorrow.

    So far I only tried to change the heating switch, but I'll look at how the hot water switch is wired to see if it's the same (I intend to replace both).
     
  9. EFLImpudence

    EFLImpudence

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    This looks like one switch cable, so that means it is likely to be coming from a place where all the wires for the system are connected.

    Have you a large junction box anywhere? Near the boiler or in airing cupboard.

    Or, indeed, can you trace where the cable goes?
     
  10. EFLImpudence

    EFLImpudence

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    What you have said explains why someone has used a double pole switch, so don't do as I said earlier and put Grey and Black in the same terminal.

    It is so that the pump and boiler are not connected together otherwise the heating will come on when you turn on the water - and vice versa.



    If you find the main wiring centre then you could have a more conventional system with a programmer for the heating and hot water including boosts.
     
  11. AndyPRK

    AndyPRK

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    This is typical of old systems that don’t have a motorised valve
     
  12. ericmark

    ericmark

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    Now it makes more sense, similar to what I had here, so hot water switch will connect supply to boiler and pump will not run, central heating switch will put a supply to both boiler and pump so it needs a double pole switch to separate pump from boiler when the central heating is not running.

    I had a timer, Danfoss3060programmer.jpg which did the job, but it needs a neutral, these [​IMG] push switches have the right idea, but instructions say only run for 10 minutes which is not long enough.
     
  13. terraling

    terraling

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    OK, I've tested everything with the multimeter, and established that there is a link between the hot water switch and the heating system switch.


    switches.jpg

    I mapped which wires are live depending on which switch is on or off, it's in the scanned sheet.

    IMG_20191015_0001.jpg

    Now to work out which to connect to the L(in) N(in) L(out) N(out) connectors of the booster switch. The timer-with-booster switch should arrive later in the week and I'm expecting it to have same connectors.
     
  14. AndyPRK

    AndyPRK

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    It’. Not simple.

    You either need a relay.
    Or a motorised valve (not plumbed in)

    And understand the wiring layout
     
  15. ericmark

    ericmark

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    I like your truth table, it seems to confirm what I thought, but still have same problem, no neutral.
    Not worked out water switch yet but rads switch is:-
    Brown feed in.
    Black pump.
    Grey boiler.

    So water switch
    Blue feed in.
    And all are clearly lines not neutral.

    So either you need a neutral, or you need a battery powered unit also it needs to be two pole. I can think of battery powered, there are thermostats that are battery powered but not two pole.

    There is likely a way, but can't really work it out on a forum.
     
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