I have lost pressure in my oil burner tankless water heater.?

I have a less than two year old Weil Mclain WTGO High Efficiency Oil Boiler - Tankless Heater. Over the last weeks or months ive noticed that my hot water pressure in my shower and around my house has gotten to the point where it is almost pressure less. Just kinda triclking out. it is plenty hot. i went down to check the pressure gauge on the boiler and it read about 20 psi. the manual says its supposed to be 50psi. any ideas or do i just need to call someone? if i do need to call someone do i call a plumber or a water heater specialist or something? thanks alot for any help.