iPad 2 spontaneously rebooting after 8.3 update

Worked perfectly well before update. Device is an iPad 2 with wifi and 3G ... not had a sim card in for a couple of years without any issues until now.

Synced and backed up manually before update (fortunately).

After update to 8.3 repeatedly recycling through reboot sequence, actually found it very difficult to power off because of the rapid cycling of rebooting cutting off the "slide to power off" option by rebooting and appearing to redo the install bar under the Apple logo.

I did a reset, redo of the Update, and then a factory state restore.

None of the above have corrected the repeated, spontaneous reboot, although in its factory restored state with no additional apps installed happens a little less frequently after it is ignored for about 30 m doing rebooting cycles (but NOT fixed).

My previously fully functional iPad 2 has been broken by the update to 8.3

Having followed all the steps recommended on other threads it appears the only recourse I have left is to take it to a Genius store.

Not impressed.