Is the cap to your water flow sensor cracked or broken? Have you overtightened the screws and stripped the tabs that hold it in place? This replacement cap will get you back running in no time. The replacement cap includes a replacement o-ring seal for the main housing. You will need to re-use your original reed switch, reed switch retainer bracket and the magnetic paddle.
While you have this off it is worth checking the condition of the magnetic paddle to see if it is in need of replacement. If your magnetic paddle is bad you will need to order that separately by clicking on this link. While swapping your old paddle to the new cap it is common for the old plastic pin for the paddle to break. You can order a replacement pin by clicking on this link.
This water flow sensor cap is designed for the older Egg style pumps use on Bestway branded inflatable hot tubs including Coleman and Lay-Z-Spa brand tubs.