Display shows LO; heater will not fire or shuts down shortly after starting.

Safety first: Turn off heater power before working on plumbing. Do not run heater without proper water flow.

• Verify pump operation: Ensure the pool pump is running at the correct speed and is fully primed.
• Check valves: Confirm that inlet and outlet valves to the heater are fully open and that bypass valves are correctly positioned.
• Clean filter: Backwash or clean the pool filter to restore proper flow. A dirty filter is a common cause of LO.
• Inspect pressure switch: Locate the water pressure switch on the header. Check for leaks, corrosion, or loose wires. If adjustable, verify it is set per Jandy specifications.
• If LO persists with good flow: The pressure switch may be faulty and should be replaced with a Jandy-compatible water pressure switch.