yep you can i did for about a week on short runs of bou two miles to work but it isnt advised other than that your heater wont work because itll keep circulating the water and wont get up to temp very fast.
if you get into bother try the kaklub forum for a run through on how to fix it the guys there are welcoming and will help as much as they can with any more problems
http://www.kaklub.co.uk/