Low Fuel Pressure Indication

Your pressure sensor is upstream of the fine filter, that’s good and also means the fine filter is most likely not causing the low fuel pressure reading.  The “other” connection on the pressure sender is an air line connected to the airbox so the sender can reference manifold pressure, that’s good. I would check that hose to make sure it’s connected at the airbox, not leaking, and not somehow kinked or clogged.  You have a bypass around the fine filter (as Rotax recommends) with a check valve, so if the filter gets clogged the fuel can bypass the filter and still flow to the engine.  

I can see that the short sections of rubber hose connecting the check valve are cracked and look quite old. Hopefully these were missed at your last 5 year rubber change and don’t represent the condition of the rest of the fuel hose (hidden by fire sleeve). The fine filter also looks older, and probably should be replaced, though I don’t think that is causing your current problem.  Stick with checking sender against a mechanical gauge as a first step. 

The aircraft is a 2020 and has a total airframe time of 220 hours. 
100 hours on the factory new engine. 
Two and a half more years until it’s first five year hose replacement. 

On closer look maybe those are not cracks in the short hose sections connecting the check valve.  They are very uniform in spacing, almost like it was manufactured that way. Maybe that is some type of heat shield covering over them.  Anyway, good luck with solving the problem and let us know what you find.  Also, just curious, what type of aircraft is it?

It is a Scoda Super Petrel LS light sport amphibious seaplane. 

Where is the proper test port to temporarily install a mechanical fuel pressure gauge? Is it on the fuel pressure regulator body?