Luminite Security floodlights stay on throughout night and daytime?

The installation is a low voltage Luminite system comprising 4 PIR sensors and 3 floodlights with a DX100 central control unit The floodlights come on at night fall and will remain on throughout the night and the day. I am able to switch them off at the control unit, and then they will remain off so long as the switch remains in the off position. I can put it back to the on position during the day and they will then stay off as they should, but again come on at night. I believe that I have checked out the individual sensors. Does any one have any ideas where to look now. Are there any devices to check the circuit/ cabling through out the house and/or the DX100.
Thanks in anticipation
KC