heater problem after installing new Rapido heater core

[mbun]

Printer Model

Trident 350

Extruder Type

Clockwork 2

Cooling Type

Stealthburner

I managed to brick the heater core on my Rapido and ordered a new one. I crimped on a JST-PH connector for the thermistor (connecting to SB2040 can board)
I turned on my Trident, started up Fluidd and immediately noticed a heater temperature of 300 degrees and smoke coming from the hot end. After disconnecting the heater I measured 24V on the heater connector, which surely isn't right.
I didn't change anything on my perfectly working printer.
Octopus 1.1 board

Please help !

 

[mbun]

Update : I measured the heater core for continuity and it showed a short, which almost certainly blew the mosfet on my SB2040 board