You need a new board. Gavin's comment above is incorrect. The t-15 will only be in you diagnostic menu if the board revision is 1.5 or later. You posted 1.33rev. And the flow switch needs to have 12" of straight pipe upstream from it and the cell can be used as this. You can install the cell anyway you want, horizontal, vertical, upside down, cord side first or not, it makes no difference.
Get yourself a new GLX-PCB-RITE. Follow the instructions that come with it and use the new wires as well. Your new board revision is wired differently than ver 1.33. The illustrations on the instructions make it a very simple replacement.