We have a 2003 Alpenlite 5th wheel. Our old fresh water pump quit working so my husband installed a new one. Now even though we don't keep fresh water in the tank (we are on city water) the tank keeps...
We had the same problem and Shurflo sent me a new check valve. Easy to put in, but a bit of a problem getting to the pump. I must have not put it back in right because it did the same thing. A fellow RVer suggested I put a check valve directly into the water line. Picked up one at Lowe's installed it. That was two years ago have not had a problem since.