DIAGNOSIS The float valve isn't sealing. Debris under the valve or a missing/damaged silicone cap is the cause.
FIX Release pressure manually by turning the pressure regulator to 'VENT'. Open the lid. Push the float valve up from the bottom to remove it. Check the small silicone sealing cap on the valve stem. Clean any food particles from the valve seat (the hole it sits in) and the valve itself. Reinstall.
IF THAT DIDN'T WORK The silicone cap on the float valve may be torn or hardened. It needs replacement. Contact Prestige customer support for a new float valve assembly.
HEADS UP Continuous steam release means pressure isn't building. Your food won't cook correctly. Don't ignore this. Always release pressure fully and let the cooker cool before inspecting.