Your wheel should not lock up. If the system was installed correctly with shut off valves you should be able to isolate the pump and see if you still have a steering issue. Have you checked the pressure in the Hynautic system?
The system has fluid and about 25psi pressure. The wheel just spins free with no rudder movement. When I turn on the NAV Pilot and put it in AUTO and turn the dial right or left, the rudder does move. When I turn it back off the wheel will still just spin with no rudder movement.
I am at the boat this morning. I am able to get the rudder to make a full travel in both directions with the NavPilot 511 unit in AUTO. When switched into standby and turned off there is still no response from the wheel. The number on the motor of the powerhead is HRP 17-12. Don't see any shut off valves.
I have seen this type of thing happen if there is air in the pump at the steering wheel. Most likely the steering wheel is located at a higher elevation than the auto pilot pump which is why the auto pilot pump works. Follow the Hynautic directions for bleeding the system and it should correct your problem.