DIAGNOSIS: The silicone sealing ring is either dirty, misaligned, damaged, or has absorbed strong odors from previous cooks, preventing a tight seal.
FIX: Remove the sealing ring from the lid's groove. Wash it in hot soapy water, stretch it slightly, and ensure it's seated perfectly back in its groove with no twists or folds. Run a steam cycle with just water to reseat it.
IF THAT DIDN'T WORK: The ring may be worn out or have a small tear. Replace it with a new official Instant Pot sealing ring. Also, check that the float valve is clean and moves freely.
HEADS UP: It's normal to see a few wisps of steam from the float valve as pressure builds. A constant, steady stream from the lid's edge means a seal failure. Never try to pressure cook with a leaking lid—it will never reach pressure.