There are three other parts on the c2 that may need replacing. 1. the reed switch (usually located close to the
fuse in the cassette locker) 2. the push button switch and 3. the pump, located inside the toilet below the push button. All these parts can be bought on line as well as fitting instructions.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix caravans/motorhomes.