Hi,
OPs diagram.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Your fritzy diagram does not show how you power the circuit or even a proper heater symbol.
A hand drawn diagram will be fine thanks.
Can you post, spec/date for your MOSFET and Heater?
Can you show what you are powering the circuit with?
Thanks.. Tom... 