Knight sensor dry wk427 - takes soo long to dry clothes ??

Hi. My Knight sensordry wk427 is taking about 160mins to dry a single load of clothes ?! You'll set it for say 80 min and when you check after the time the clothes are still damp so you have to put it on again. Anyone got any ideas ??? Seems as if it's not getting hot enough or something. Could it be a sensor problem ??? Do you think l should just give the thing a damn good clean out ?? Any advice would be great. Thanks