I tried to do this just now and their site stopped working so I'll go from memory.
Go to Volcano's website and login to your account. Under "my account" should be a "customer service" tab.
There should be a button or section to report a problem. Simply type what you're having trouble with and hit submit.
They'll email you back asking you a few questions or they'll email you a repair/replacement form along with a prepaid USPS label.
I had trouble printing the form. It would print the border of the document with the Volcano logo but everything else was blank. I took a screenshot and printed it. FILL OUT THE FORM, put it in a padded envelope with the Lavatube, attach USPS form and mail it to them.
You'll get an email 5 or 6 days later saying your device is broken and they're mailing you another one. Easy as that.
I've done this twice because my original blue one started acting funny. They sent me a gray one and it didn't work at all. They immediately sent me another blue one and I'm using it right now. I have blue, red, chrome, and pink (GF's) Lavatubes. I use them and lend them to people regularly and only one has broke. I can't complain since they only cost $80. I beat the crap out of my Provari every day and it takes it without flinching. Big price difference though.