Solid FL or FLO mean on of 2 things. By far the most common is that the pressure switch has failed. You can adjust but experience says that adjusting will only work temporarily, if at all.

To confirm its the pressure switch, do this. Turn off main power. ID the heater. It's the steel tube strapped to the back or bottom of the control box, a steel tube that goes through the control box, or to left of the control box. It looks generally like:

or

If the heater is strapped to the back or bottom of the control box, the pressure switch is screwed into the left backside of the heater. You will see 2 wires coming out of it.

If the heater goes through the control box, the pressure switch screws into the top center of the heater (you will need to remove the control box cover to access).

In either of the 2 above cases, unplug 1 wire. Turn on the spa. If the pump comes on then you confirm the pressure switch at fault. If not, the pcboard itself has failed. Failure of the pcboard is rare for this but can happen.

If you have the heater to the left of the control box as shown in picture to right, your spa uses a flow switch. You will notice on the upper pipe leading out of the heater is a switch with 2 wires coming out of it. You will have to remove the cover on the control box and follow the wire to where it plugs into the pcboard. Unplug and secure the wire. Like the pressure switch test, turn on main power. If the pump comes on, you need a new flow switch. Flow switches can't be adjusted. If you get a Solid FLO error code you first start with replacing the flow switch. Flow switches can not be adjusted.

You will find these switches at:

Click Here

Click Picture