Coming home from our summer trip the water pump began short cycling when no water was being used. I traced it to a small broken part in the valve used to fill the fresh water tank. The part would sometimes lodge in the seal, preventing it from sealing completely. I received a new valve & today replaced the innards. I decided not to change-out the valve body, didn't want to tangle with the 5 year old pipes.
Here is the new valve:
Here are the innards, new one is on the left:
Here are the innards without the rubber valve seal. Notice the new one on the left has 4 prongs, the old one has 3. It was this broken 4th prong which was causing the problem.
All good now.
As soon as I resize some pics I will post what the black tank toilet & vent grommets that I just received look like.