Hi niko1522,
The Output Pressure Gauge on the side of the pump will only display a pressure while the pump is running and high pressure water is exiting the nozzle. It seems like either the pump is not running or water is not exiting the cutting head when this picture was taken! Is that correct?
Run a Nozzle Purge - this will turn on the pump and open the HP Valve in 3 bursts followed by one longer burst to allow high pressure water to exit the cutting head. Does this gauge reach 4000 psi during this check?
If the gauge is still not displaying any pressure reach out to us at support@wazer.com and well help to get you back up and cutting!
Thank you,
-Greg