I have just replaced the non maintained emergency lights at home everything fine for 2 weeks, however I have 1 unit that now is permanently on even though the green neon light is lit and there is no power failure. I have switched the power off and on but the light remains lit. Why is this

 

Many modern LED fittings are dual purpose and can be set up for either maintained or non maintained mode and it sounds like the unit is in maintained mode, although if it wasn't lit when you first installed it I can't see how it's changed just sat there!