Elec toilets are a pain that's why I'm sticking to manual after having problems with electric ones.
May be damp switch you could try hair dryer over switch in any case follow ins below for Thetford repair pdf's free. Then access the switch again try hair dryer gentle setting air flow mid temp. also try smear vaselene (petrolium jelly or spray siclone on switch button it may be sticking.
www.thetford.com.au for Australians.
www.thetford-europe.com
On home page click on Products
Click on read more (Toilets)
Click on read more (cassette toilets)
Click on read more (C200)
Click on Service
Click on pdf Repair instructions- sanitation
Save file to computer then on disc for reference when in caravan obviously with DVD/CD player.
As the cassette is the same this refers to the C200 but still download the pdf file.
Still having problems look out for 'Ask thetford as you run through the site.
bob, March 2012