Start by preparing the ingredients. Chop up the onion and the celery. Cut the potatoes into large chunks - peeling is optional, just make sure the skin is clean if not peeling.
Place the stainless steel pot inside the Instant Pot. Add the onion, celery, and potatoes. Then pour in the vegetable broth and then the frozen corn. Place the frozen cod fillets on top of the veggies.
Lock the lid in place. Close the pressure release valve and press the “Pressure Cook” button until it’s on “Normal” and press the “Pressure Level” button until its on “High”. Press the +/- buttons until the display says 00:05 for 5 minutes.
While the Instant Pot is cooking, mix together the water and cornstarch in a small bowl.
When the time is up, allow the pressure to naturally release for 10 minutes (just leave the Instant Pot alone and let it count up for 10 minutes). Then press the “Cancel” button to turn off the Instant Pot and quick release the remaining pressure by opening the pressure release valve, staying clear of the steam.
After the pressure is released and the float valve falls, remove the lid.
Turn the pot back on “Saute” and bring to a boil. Add the clams, including the liquid. Mix up the cornstarch and water mixture one more time and then add to the Instant Pot, mixing in well. After the soup has thickened, press “Cancel” to turn off the Instant Pot. Then add in the heavy cream, garlic powder, thyme, and salt and mix together well.