Balboa VS501Z System 5.5Kw Spa Pak 54356-03. This item is discontinued and no longer available.
VS501Z is discontinued by Balboa, see the new complete BP systems...
Balboa VS510SZ 5.5kw Spa Pak 54371-03 is the previous version of the VS510SZ spa pack with case, circuit board and heater. New model released now has a 4kW heater and is VS510SZ - see G4154