In my coach, there is no valve inline valve external to the pump. But, there is an extra check valve external to the pump. I guess it all depends on who was assembling the plumbing at Redwood the particular day your unit was being built.
The check valve in the pump can be replaced, at least on mine (SHURflo pump). It may be easier for you to just add the external check valve or the inline, quarter turn pex valve.
My guess is that there is some debris that has lodged in your pump check valve. You may be able to clear the debris by turning the pump on/off several times while running some what in the trailer.
You might also try getting an "air to hose" adapter and use a compressor to force low pressure air backwards through the pump towards the tank to see if that would clear the check valve. Just be sure not to apply too long or at too high pressure..........you don't want to damage your fresh water tank. I would drain the tank and leave the drain valves open while doing that operation.
Guy & Phyllis
2012 RW36RL,DualA/C,KodiakDiskBrakes,TrailAir Tri-Glide,GY_G614's,Roadmaster Comfort Ride Slipper Spring Suspension
2011Dodge3500Laramie,CrewCab,4x4,SRW,Michelins, LongBed,6.7LCTD,3.73,PullRiteSuper5th20.5KHitch, BlueOxBedsaver