I think i found the problem.
The subtank base had come apart slightly meaning the bottom of the coil deck wasnt making proper contact with the copper pin
Seems better for now but maybe its better to get a new base just in case.
Noticed an extra 2mm gap above airflow ring..... Took it apart, cleaned it, rebuilt - okay at the mo
Theres a tiny ballbearing in there that I'm amazed hadn't fallen out. Was damn lucky