I started with a full tankless diagnostics , checking everything from its power source and all of the internal components while turned on and turned off, also checking the water supply to the unit and the temp that the water was getting up to. What i found was that the electric tankless water heater was operating correctly. Since it wasn’t the tankless causing the low water flow I started looking in to the water pipes and fittings after the tankless. What I found was a bunch of debris built up in a gate valve that was between the pex pipe and the tankless flex supplies. I cut this valve open and installed a full port ball-valve so that debris can not ever build up again at this point and also cleaned up the bent pex water pipes.