The induction heater was tested using a relay as an ON-OFF switch before and worked so i just want to focus on the MOSFET switch part of the schematic.
When i tested the circuit using a MOSFET switch it worked but after a few tests the OFF state just stopped working. After taking a look at the P Channel MOSFET I noticed that it was always ON even with everything turned off. I suppose something must have burned the MOSFET.
And my question is what may have caused this to happen?
It's probably inductive kickback when you switch the PMOS off. Put a diode in there; cathode to PMOS drain, anode to ground (so it's reverse-biased when the PMOS is on). When you turn off the PMOS the two inductors will pull current from ground until they're discharged.