That sounds like what both of my bad pumps did. First they would not turn off. The next day there was no pressure. With the news about WRV, I would suggest you go to the Shurflo website and contact them to find a place to exchange your pump, since it is under warranty. The pump has a date code on it, so they will know that it is under warranty. They exchanged mine, no questions asked. They took it apart to check it out, and gave me a new one. They even tested the new one before they gave it to me.
Good customer service. Unfortunately it appears they need it!
'04 Alpine Coach 36' MDDS