I am picking my coach up from the shop this morning after experiencing exactly the symptoms you have. A sharp mechanic realized when he moved the pump he got less flow into the filter screen by the pump. He undid the hose and followed it back, and a foot up the hose he found the line was kinked. He took the twist out of the hose and said it now works great.
This is a new coach and I was not able to test the pump system because it never got above 20 degrees from when we took delivery until we headed south. If yours used to work you should see if your screen needs cleaning.
Dave