old (20yrs) White Knight dryer?

The machine is not drying loads properly. Had back off looked at element when machine on. Does the whole element glow for full heat and only half for half heat ? We have recently had new kitchen and the dryer is now enclosed,however it was enclosed on both sides before, with the front exposed, and it is in the same position. I always leave the door open when using and there is about the same gap around the sides as before, but it does seem as if the fault has occurred since the new kitchen.