I got the same issue! The tank never gets up to full pressure, and the pump runs until the internal temp sensor trips it off. It lost one leg because of a bad Pressure Switch up by the tank. One leg of the 240 was grounding out against the wire tension clamp.
Heres the link to the details..... Coffee 3-17-2012
We are limping along on low water pressure, and complete loss of water pressure, until the new pump arrives.
Our new Grundfos pump will be here friday.
I'll install it Saturday.