Help installing LW920 Boiler Switch

LightwaveRF Community: Welcome Forums Installation and Troubleshooting Help installing LW920 Boiler Switch

This topic contains 4 replies, has 4 voices, and was last updated by  michael ward 9 months, 1 week ago.

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     LogiBear says:


    I’ve swopped thermostat’s before, but my recently purchased LightwaveRF LW920 Boiler Switch has me scratching my head. My thermostat controls my hot water and my heating. The current Thermostat has the obvious neutral and live wires, and then wires leading into terminals marked Domestic Hotwater On and Heating On. Which terminals should these two wires connect to on my LW920 boiler switch ?

    My attempts to understand the Normally Open, Common and Normally Closed terminal arrangement has left me with a head ache. So any assistance would be gratefully received.

     nevetsecirp says:


    My understanding (as I haven’t fitted the boiler switch, but was going to so read up on the wiring diagrams etc) The LWRF boiler switch will only control 1 channel eg heating, if you want to control 2 channels eg hot water as well you need another relay / switch

    LWRF light switches in several rooms, WIFI Link, Energy Monitor, Socket x3 and multiple On/Off adapters. PIR controlling lights and doorbell utilising light feature. TRV's for heating. Relays for garden and outside lamps Linked with Amazon Alexa via a dot
     madlou says:


    You will need the LW920 for the Heating, and maybe a LW934 for the Hot Water. I have just completed this myself.

    For the LW920 – I followed Adam123s advice here –

    For the LW934, the layout is different, but I followed the same principles.

     michael ward says:

    michael ward

    Doe anyone know what the P terminal is on the boiler switch LW920
    Connections are earth, N, L, L, n/o, com, n/c, and P?

     michael ward says:

    michael ward

    I have decided to revamp my system with the addition of a SPDT relay. I would add a drawing if anyone requests it but my solution to the above is quite simple.

    A LWRF switch is used to turn the boiler on or off, for boiling the water, which just leaves the problem of the Zone Valve and pump for central heating.

    A Single pole double throw relay is used to achieve this. The switched output(N/O) from the thermostat is wired directly to your zone valve and pump. A relay is then attached in the following way. The switched mains is attached to one side of the coil, with the other side of the coil to neutral. The switch contacts are wired so that the boiler is connected to one set of the N/O contacts and the pump/zone valve to the common.

    Whenever the Thermostat is triggered, power is sent to both the boiler and zone valve/pump.

    When the thermostat is not in use the boiler can be turned on as normal via the LWRF switch, which in turn can be programmed with your on/off times to suit you. I don’t see any need for a flywheel diode in this case, as switching is slow, but a suitable suppressing resistor capacitor should be used across the relay contacts to minimise arcing. Typically 47R(1/4 W should be enough) and 100nF capacitor in series across the contacts.
    I think you can pick up suppressors for relays, easily enough.

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