Not sure best ask Thetford www.thetford.com then contact us and email them but don't hold your breath they aren't very quick replying. Or have a word with your local caravan repair workshop.
Bob
December 2008
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix caravans/motorhomes.