If you are using the UH8-RF or UH8-RF V2, ensure that the aerial is pointing upwards.
As a repeater, you can use either the Heatmiser Boost or the neoPlug as a repeater. Just plug it in between the thermostat and the receiver, there is no need to add it to the neoApp and do not worry about the lights on the neoPlug. This would also apply if you are using a neoAir without the neoApp or a Touch RF.