Canon EOS 500D Flash problem

Even an external flash apparently has its limitations. This from the 430EX II Manual (Page 7):

"To avoid overheating and degrading the flash
head, do not fire more than 20 continuous
flashes. After 20 continuous flashes, allow a rest
time of at least 10 min.

If you fire more than 20 continuous flashes and
then fire more flashes in short intervals, the
inner overheating prevention function may be
activated to make the recycling time about 8 to
20 sec. If this occurs, allow a rest time of about
15 min. and the flash will then return to normal."

Perhaps a defect in flash temperature sensor (camera or external) could cause the delay feature to activate (i.e., "busy) after fewer cycles.
--
Editor Bob