I have been dealing with this exact same issue for some time now, I bought the ZNA brand new towards the end of April, and one week after using it the auto firing issue started. In my idiotic and frantic attempts to reseat the board by pressing on the button and the top seal on the back of the DNA module I pretty severely screwed up my ZNA's body and finish.
In deep despair I sadly sent it in to HOH expecting the worst, but barely 2 days later I got a call from Zen himself. He was an incredibly gracious man, and felt bad about my super frustrating experience, and as such, he sent me out a replacement model, essentially a refurbished ZNA, at absolutely no cost to me. He may not have his designs perfected to the point where they are completely bug free, but he is a seriously solid guy when it comes to how firmly he stands behind his products.
I sent my ZNA off to HOH on a Tuesday, talked to him on Thursday, and had my new replacement model in my mailbox by Saturday of the same week. What really busts my balls though is the fact that the replacement ZNA, having performed perfectly for a solid 2-3 weeks, just started having the exact same firing issue about a week ago. This, as you can imagine, is insanely frustrating, but I will tell you, after the experience I had with him servicing it before, I am supremely confident he will gladly fix it (hopefully permanently) yet again for me.
If you want my advice, take some deep breaths, grab your 2nd favorite mod to use for the next week or so, don't try to mess with the ZNA, and send it directly off to HOH. His design, or perhaps the DNA30's design, has a severe flaw, and in my mind, it's not worth the risk of voiding your warranty trying to DIY fix it yourself when you have a solid warranty service that, from my experience, is very dependable and very fast.
The real ..... for me though is that after a week-ish of sitting by itself, not being used, the night before I was going to send it off to HOH, I resecured the body tube threads, and now she's been working perfectly for the past 3 hours. I want to believe the auto-firing won't come back, but my previous experience tells me I shouldn't hold my breath. **Sigh** I'll comment again if I run into more issues.