We had a similar problem on our 2018 Hawk last month, camping in Great Sand Dunes NP, fairly cold temps. I think our water was a little low at the time but I can't remember. When we set up camp, I turned on the water pump and it kept pumping. I got decent pressure at the faucet, maybe a little less than normal. But the pump kept running. I thought there was a leak and kept looking for water to come out from under the cabinets or in the truck bed somewhere. No water ever appeared so I ruled out a leak. But I could not figure out why it kept running. The valves were all in the proper place. It was getting dark and I was a little flustered, and I went outside to see if there was anything obvious that I missed. While my mind was working on the problem, my hand decided to reach up and open the filler cap. As soon as I had the cap off, I realized that the cap had felt a little weird coming off, like it might not have been screwed on all the way. I replaced the cap properly, and turned the pump on again and it was back to normal.
I have a fair knowledge of house and irrigation plumbing, but am woefully ignorant about the system in the camper. So I don't know if the cap being off would cause a pressure leak to keep the pump running. It sure seems like that is what it was, but how can the filler cap keep pressure in if there is a constantly-open air vent right there to allow air to escape when filling the tanks? Until I learn otherwise, I believe that that filler cap needs to be firmly sealed or the pump may stay on continuously.
