Check valve

A check valve lets water move one way. Pool systems use it near heaters, chlorinators, and spa setups to keep hot or chemical-rich water from flowing back into equipment.

A worn valve can leak, chatter, or stick. Signs include water draining from the pump when it is off, noise, or chemicals backing up. Replacement requires cutting into pipe, so a pro should do it. Skipping a needed check valve near an inline chlorinator can damage equipment.