[TC issues with DNA 75]

VapingBad said:

This does sound like a connections issue, IIRC the outer of the 510 on the nano unscrews, take it out, clean both side of the threads and replace it securely, you get the same issues with threads on mech tube mods.  Also some of the VT75 have a ground screw or two on the base, again check these are secure.

Eureka! 

I removed the head 510 and there was condensation of liquid below. I also cleaned the threads well. So far it works well.

Thank you very much!

[TC issues with DNA 75]

VapingBad said:

This does sound like a connections issue, IIRC the outer of the 510 on the nano unscrews, take it out, clean both side of the threads and replace it securely, you get the same issues with threads on mech tube mods.  Also some of the VT75 have a ground screw or two on the base, again check these are secure.

Thank you, VapingBad! I will check that.

[TC issues with DNA 75]

I have the same problem with VT75 Nano. I have installed the newest firmwares.