Hi, sounds like the one way valve at the city/shore water connection is not stopping water flow when you are running on pump from the fresh water tank. That is just like having a water tap open. The water pump will run continuously if it cannot pressurize the high pressure (taps) side of the pump or for other reasons (like air leaking into the low pressure side of the pump; etc). You could try to turn off the pump and use shore water again to see if you can clear any blockages in or near the one way valve at the shore water connection.....then go back to pump water (disconnect your shore water hose and see if water still comes out the shore hose connection on the coach. You might need a new one way valve/shore water connection.
Good that you are checking your filter screen on the low pressure side of the pump. The bits are usually from when Thor cores the fresh water tank for water line connections. Sometimes when the cap is replaced on the filter housing it (or filter body) can leak air or get cracked from over tightening etc.....in which case air gets sucked into the pump and it won't prime or flow properly and will also run continuously.
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