Temperature gets stuck.

So I was starting a print and all was fine, then the temperature hit 177° then stopped. I waited a second then saw the PETG boiling on the nozzle and I knew something was wrong. I cut the power and when I turned the printer back on, It reported ~400°.

I would like to get this problem fixed as soon as possible as I value my house not being burned down. Anyone know what's going on here? Any help would be appreciated.

your thermistor wires for your hot end are shorted togeather

Often this is the screw holding the thermister in place is shorting them, or the thermistor legs are twisted together and touching

Some times it can even be the controler IO pin has died... (swap the bed thermistor on to the hot end plug and verify it reads room tempature (or close enough) , then swap it back before you forget)