Add bones, onion, carrots, celery, peppercorns, parsley, thyme, and water.
Close and lock lid. Set the pressure cooker to "soup" and adjust the time to 20 minutes, and press "start/stop".
Once done, let it naturally release its pressure. When all pressure is released, do a quick release to make sure all pressure has been released before opening the lid.
Strain the stock through a fine mesh strainer or cheesecloth.
