Balboa GS501 series PCB.

Fitted to the GS501SZ spa pack.

Note - for identification there is only ONE code on the board you need to identify this board. This code is on a sticker on the side of the transformer and will clearly state 54516.

This will be fitted to the pack 54515.

It is very important that you check to see if the codes you have show an "S" in the numbering. The 501SZ pcb is NOT the same as the 501Z pcb.