There are both wireless and wired versions of the TIME:O:STAT available. If you are replacing an existing wired thermostat then we recommend fitting a wired version. A wireless version may be better If you do not currently have any thermostat wiring and can not easily run a wire between where you want the thermostat and the boiler. For wired versions: check if you have a 2 core wire or a 3/4 core wire. If you have a 2 core then order a battery (2 wire) model. If you have a 3 or 4 core wire then order a mains (2 or 3 wire) model. If you you have a hot water tank and do not have an existing timer for the hot water, a 2-channel TIME:O:STAT will allow hot water control.