Tumble dryer heat cuts out?

Hi. We have a Whirlpool AWZ7914AL tumble dryer. When you first start it up, the heater elements kick in but as soon as the get red hot, they cut out, but, the dryer keeps going. If you start it up again immediately, once again they glow red and shut down and as before, the dryer keeps going. I do not suspect the thermostats are at fault, because you do not have to wait at all before stoping the dryer, then restarting it to make the elements heat up. What is the likely most fault please? Thank you.