If it's intermittent then it's almost certainly a slight water leak.
I used one of these years ago, and in fact it's still in the back of
the shed. They use a Haden 2kw kettle element. Eventually the seal
will leak slightly allowing some seepage onto the plug connector, this
also causes condensation problems which can wreak havoc with the
Vac motors. Worst case scenario about £70 - £80 to replace element
and motor.