diconect the safety switches from the cassete holding tank thay are only there to stop any one using the toilet when holding tank is removed or you can buy 2 new switches from lesiure shop direct web site
doxy, April 2012
Have you checked the 3a fuse?.Check Thetford website
http://www.thetford.com/HOME/PARTS/PermanentToilets/CassetteC2ElectricPartsNEW/tabid/644/Default.aspx