could be blocked up at the bck where the pump is theres a trip switch in side with a float made out of polystyrene , if the frount red lights on it means resivouirs full and the tray needs emptying so it wont let the heating element switch on , be carefull as the switch terminals are live so be warned ,make sure you have cleaned out all bck of the heat exchanger , (lot of it is common sence not rocket science like domestic engineers make out , ) it vents are blocked moisture blows back in to the heating elements and trips the sencors , dry out with hair dryer and try again ,, :)
philip roy kernot
December 2012