If you just replaced the pump and the pressure switch, it is most likely one of two things.
One, you could have air lock at pump one from replacing it. Then it wouldn't allow the water to flow through, and causing the flow error code. You could tell if this is what is happening as there would be no water shooting out of the pump 1 jets. Do free up the air lock, just loosen the union in front of the pump one to let the air out, and then hand tighten it back up once you hear the water shooting out of the jets.
If the water is shooting out of the jets, and its not a air lock, then the pressure switch just needs to be adjusted. This is the switch that threads in in top of the heater barrel. It will either have a small black turn typed daisy wheel. Just turn it a quarter of a turn at a time until the error code goes away.
Or, it could have a small screw type head, like a flat head screw. Use a flat headed screwdriver to turn it a quarter of a turn at a time until the error code goes away.
One of those should fix you up. If not, call your dealer, or reply back here, and I will try to help.
