Not sure if you did this but I would consider turning off the pump, relieving all pressure in the system and trying to drain water out of the hot water tank through the piping.
Another thought is to actually drain the hot water tank and if you can, flush it with some fresh water. Maybe connect to city water while drain open and let it flow out the drain hole.
The reason I suggest this you may have some junk in the system.
2017 SLX 195RB
2014 Jeep Grand Cherokee Overland, gas 3.7 V6
Andersen WDH hitch
Dometic Milenco Aero mirrors