When we got our Siesta sprinter in March, we had lots of similar problems with the tankless water heater. Our problem ended up being with low water pressure when hooked up to city water. They had us test it by running on the pump rather than city water. We found that ours worked fine that way. Our pressure regulator was reducing the pressure too much. We bought a new adjustable one and have had no other issues.
Am not sure of the valves mentioned. The valve to switch from city water to pump, etc is in the back outside bay.
There are several threads on this site discussing problems with the tankless hot water.
Good luck.
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