Oh dear these Chinese saying clones are a cavalcade of issues. It could be the 510 pin isn't making contact with the mods 510. Is it manually adjustable. If so raise it if not try undoing the 510 pin in the rda half a turn (making sure the coil deck remains stable). If not check to make sure the switch copper is making good contact when you press the fire button.
Do you have another rda you can try on it bud. Either the 510 is not making contact or there's a production issue.
May be worth a pic of the internals too. Just to see if we're missing something obvious. They are simple but full of possible issues.
good point old boy yes that would help alot
Check to make sure the copper strip that's pushed with the switch isn't hitting the plastic spacer ring situated on the 510 in the mod or it isn't poorly shaped and hitting the top and bottom of the 510 (hitting both above and bellow the plastic spacer) it should only touch the bottom section when pressed. Also it sounds daft but be sure the battery is put in with the positive side downwards.
