Diagnosis
The unloader valve is stuck open or the inlet water filter is clogged. Low inlet flow causes no output pressure.
How to Fix It
Check the inlet filter first. It's in the water inlet connection. Unscrew it, clean any debris. Then check the unloader valve. On the AR383, it's on the pump head. Remove it, check for a stuck spring or debris. Soak it in vinegar to dissolve scale. Reinstall.
If That Didn't Work
The pump's ceramic plungers or valves may be worn. You'll see water leaking from the pump oil sight glass if seals are gone. That means a pump rebuild or replacement.
Heads Up
Never run the pump without water flowing through the inlet. Even a few seconds dry can score the ceramic plungers and wreck the pump.