Ender3 pro v2 hotend thermal runaway

good morning, can someone please help as i mentioned above i have a strange thing going on with my printer. when i switch on the hot end immediately starts to heat up climbing to the temp where it cuts out on thermal overheating . this only started when i replaced the hot end

Did you remember to put the silicon boot on the new hotend when you installed it? Had that happen to me once on one of my V2’s.