Wiring for Hot Water and Boiler

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LightwaveRF Community: Welcome Forums Installation and Troubleshooting Wiring for Hot Water and Boiler

This topic contains 4 replies, has 3 voices, and was last updated by  mrashton 1 month, 2 weeks ago.

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  • #25055
     TheCaptain says:

    TheCaptain
    Participant

    I’m trying to wire in the LW920 boiler switch and use a LW934 switch to control my hot water on what is a Y Plan system. After eventually unjumbling the mess of wires that greeted me, and transferred it over to a nice neat wiring centre I’m a bit stuck as to how to replace the Programmer (a failry old timer manual timer) and thermostat with the two new switches. I’ve attached a diagram of the wiring centre, and the new available connections.

    Without removing the original timer, the boiler switch seems fairly self explainatory – I’m assuming the Live feed (D) would be straight from the mains (ie box 11 on the Wiring Centre), COM (F) would match up to the original live feed to the themostat (3) and NO (E) would go to the Switched live from the thermostat (2). However removing the timer would I just join the L->COM to make it work?

    I’m drawing a bit of a blank on the Hot Water though – I’m assuming the Live Feed (A) can come from the mains, but where should I connect B and C?

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    #25074
     mrashton says:

    mrashton
    Participant

    I too would like to add the LW934 to control the hot water in a Y plan heating set up. LightwaveRF, we’d appreciate some guidance wiring this into the standard Y plan wiring centre please. (Or anyone else who’s managed to get this to work).

    #25185
     mrashton says:

    mrashton
    Participant

    So after some thought and consideration I found that you can’t use the LW934 Electric Switch to control the Hot Water in a Y Plan heating configuration. This is due to the LW934 switch only having a COM input and Switched Live output when, to control the Hot Water in a Y Plan set up, you need to have a switched live when the Hot Water is ON and you need a separate live feed when the Hot Water is OFF – This is needed to energise the GREY wire from the Midpoint Motorised Valve for the SAT (satisfied) status.

    I searched all of the literature for the LW920 Boiler Switch and it states that it only works with a LWRF Thermostat linked to it which made me think that the Lightwave Link couldn’t control the switch separately. I was wrong and also, the LW920 does have a COM input, a switched live or NO (normally open) output, AND a NC (normally closed) output. So, when the LW920 switch is ON, the relay switches on the link between COM and NO, and when the LW920 switch is OFF, the relay switches on the link between the COM and the NC connection. This is exactly what is needed for the Hot Water to function in a Y Plan.

    I was a little concerned about using this with a GEN 1 Lightwave Link as I assumed it would not be configurable but it does work. I paired it as an Electric Switch (there is no stand alone Boiler Switch option) which worked fine and then for the Heating Schedule you are given the option to either select a temperature for each time schedule or you press the little icon with 2 opposing horizontal green arrows and the screen changes from temperatures to select from to the selection of a simple ON status and an OFF status.
    For some reason you still have to set a Set Back temperature so I’ve set that at 0.5 degrees for each day and then set the ON/OFF schedules as follows:

    (I cook the hot water for 2 hours a day)

    06:00 – 18:00 OFF
    18:00 – 19:00 ON
    19:00 – 21:30 OFF
    21:30 – 22:30 ON
    22:30 – 06:00 OFF and this completes the 24 hour cycle of events.

    It works perfectly.

    - @TheCaptain, I’m sure by now you’ve got the answers to your questions as it’s a month later but to answer your wiring questions:
    D – yes – connect directly to the Live input at the wiring centre.
    F – Connect a bridge from D to F in the Boiler Switch which gives switchable power to the switch.
    E – This will connect to 2 in the wiring centre – Energising the White – CH Call for heat – at the Motorised valve.
    These connections replace the need for the programmer.

    For the Hot Water, as I mention above, you need another LW920 boiler switch to give you the additional NC connection (over the LW934 switch) needed to energise the Grey wire of the Motorised Valve when the call for Hot Water is OFF,
    So the 2nd Boiler Switch is wired the same as for the CH Boiler Switch but the NC connection is connected to 8 on the wiring centre and NO is connected to 10.

    I hope this helps someone but if confused please just ask.

    #25231
     caldirun says:

    caldirun
    Participant

    I used the in-line relay LW821 to control the hot water, it has 2 outputs Open and Close plus a Stop which de-energises both outputs. You just need to set a couple of timers, one to Open then one to Close after your required time interval.

    #25236
     mrashton says:

    mrashton
    Participant

    I used the in-line relay LW821 to control the hot water, it has 2 outputs Open and Close plus a Stop which de-energises both outputs. You just need to set a couple of timers, one to Open then one to Close after your required time interval.

    I considered the relay but wanted to maintain the manual “Boost”and On/Off functionality at the physical switch. The Boiler Switch works perfectly in this situation and you get the added bonus of a thermometer in the airing cupboard :-)

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