Reactor and Gusmer Products
Reactor 2 : E‑30, E‑XP2
T4DB : High Temperature B
Bad RTD or bad RTD placement against heater
Swap A and B heater output cables and RTD cables and see if issue follows. If so, replace RTD.
Flow too high for temperature setpoint, causing temperature overshoots when gun is de-triggered
Use a smaller mix chamber that is rated for the unit in use.