How do you replace a flow switch in a spa, or hot tub

Turn off the power to the spa. remove the cabinet under the topside remote to expose the equipment compartment. You should see the flow switch, it's usually a threaded 3/4" plug with a single grey wire coming out of it. Most of them are threaded into a tee or a special transparent fitting. If the water level in the spa is above the flow switch, you may have to drain the spa down unless you're very fast about getting the new switch in. Unthread the old switch and thread the new one in. Follow the wire on the old one to the spa pack. You'll have to remove the screws on the cover to expose the circuit board. Follow that wire into the spa pack to see where on the circuit board that it is plugged in. It may be good to run the new wire to have in place as soon as you unplug the old one you can install the new one with no question as to where it plugs in.

Reinstall the cover on the spa-pack and turn the main power back on. Make sure that the arrows on the new flow switch are facing the correct direction (direction of flow). Once you have the spa on and it starts back up, run everything to check for leaks and proper operation. If the flow switch was the only problem, all your faults should be cleared and you should be in good shape. If there are no leaks, you can reinstall the cabinet panel.

The new switch should already have teflon tape on the threads, if not, use teflon tape, apply the tape in the direction as if you were threading a nut onto the threads. You only need a few wraps of teflon tape, too much can crack the fitting you threat the new flow switch in to.