I received my full size Rainbow Heaven last week from an ebay seller. It seemed that when I completely assemble the RBA, I couldn’t get the top stainless steel threaded end cap to lay flat on top of the quartz tank. The cap of the evaporation chamber pulls the top stainless steel threaded end cap up about 1mm.
I have 18 different kayfun’s and have tried several different models, but I got the same result. My suspicion is the larger quartz tank (not the nano) had been cut about 1 mm to short. I could have probably got this to work if I trimmed about 1 mm from the cap of one of my Kayfun evaporation chambers; however I hesitated to modify an existing unit.
The seller agreed to take the unit back and refund my money, so I returned it today.
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I had the exact same problem with the Rainbow Heaven tank that I bought off eBay when I put it on a KFL+--when assembled the top cap would seat properly on the chimney, and it just kept popping apart.
Like you, the seller was very gracious, and accepted a return with a full refund.
I was happy with his customer service, but bummed that this tank wouldn't work with a legitimate KFL+...
Now I'm waiting for the "Science of Vaping" website to come back up, so I can order one of their V2 glass tanks--seems to be a FAR superior design, since it comes with a replacement chimney which actually THREADS into the cop cap, rather than just seating into it with an o-ring. But the SoV site has been down for about a month, and I'm starting to worry they might never come back online... :-(