Let me make sure I understand:

1. The cell has been in service for 4 years.

2. The only fault is lack of chlorine production.

3. You have occasional, or regularly, used the BOOST mode.

Is that all correct?

If so, is there reason you aren't thinking that the cell is simply at the end of its life? Are you aware that SWCG cell life is pretty much a straight forward function of "ON" time? And that BOOST mode results in significantly reduced cell life?