I have a subpanel feeding off a 50 amp breaker. The subpanel contains a GFCI 50 amp breaker which is connected to a new 32amp spa heater. When I flip the GFCI breaker on for the heater, it immediately trips the main 50. Nothing else is connected to the subpanel and the GFCI itself doesn’t trip. I have pulled 40amps from this subpanel while charging my EV.
The spa heater is a Balboa VS501Z.
Any thoughts on what I can check?