I've just done this with a few of my supers after advice posted by Finman last year. It works a treat.
I uncapped the frames, lined them up in a large plastic storage box, carried them upstairs to the bathroom, used the shower attachment to gently wash them over with warm water, filled the plastic box up with water, put a heavy weight on the tops of the frames to keep them submerged.
Et la voila...... 24hrs later the crystallised honey had all dissolved out.
Just use a sieve to make sure any fragments of wax don't go down the plug hole whilst draining the water away.
They are drying off now, all ready for the amazing season that I just know we are all going to have