Aquabion softener shows E05 and no water flows through the unit, or flow is severely restricted.

Safety first: Turn off power. Close inlet valve and open a downstream tap to relieve pressure.

• Check bypass position: Verify that the Aquabion bypass valve is in the correct "Service" position. If in bypass, move it to service and check flow. If the handle is stiff or does not fully move, the bypass may be damaged and require replacement.
• Inspect inlet/outlet valves: Remove the inlet and outlet unions and check for debris or scale buildup at the inlet screen and outlet check valves. Clean screens with a soft brush and water.
• Test solenoid operation: With the unit reassembled and powered, start a manual regeneration and listen/feel for the inlet solenoid valve clicking. If there is no sound, check the solenoid coil resistance with a multimeter (compare to Aquabion specs). Replace the solenoid if open or shorted.
• Control board check: If the solenoid tests good but is not being energized, the main control board output may be faulty and require replacement.

Warning: Use two wrenches when loosening plumbing connections to avoid twisting copper or PEX lines. Always check for leaks after re-pressurizing the system.