Originally Posted by TerryDM
That's good advice there. I didn't even think about getting a test done. That should definitely be your first move.
water pressure can be tricky as many factors can contribute to the overall picture.
What is your gpm flow before and after tankless? There is a manufacturer specified range that unit will work best with also unit may be clogged. Scaling can build on interior heat exchanger surfaces and constrict flow volume. Other factors apply but more information is needed.