I would be very interested to know what model it is as I have a C2 bench type toilet with electric pump in my static and in the tourer a manual flush and with both you have to open the blade, as it's refered to, manually. The electric flush,as you question implies, does not open the blade automaticlly.
If it's one that opens on flushing please post the model as I want one. If you mean the blade refuses to open on turnign the large flush knob the go to www.thetfor-europe.com or www.thetford.com.au for Australia and look for 'Ask thetford ' then ask them why you can't turn the knob to open the blade. It also has great pdf downloads.
bob
June 2009