Display shows FLO or FL0 and the Raypak unit will not run the compressor or heater; may click but not start.

Safety first: Turn off power to the Raypak unit and the main pool pump before opening any plumbing unions.

• Verify pump prime: Make sure the main pool pump is fully primed and running with a solid stream of water in the pump basket (no large air pockets).
• Clean the pool filter: Backwash sand/DE filters or clean cartridge elements thoroughly. A dirty filter is the most common cause of FLO on Raypak systems.
• Check valves and bypass: Confirm suction and return valves are fully open. If there is a manual bypass around the Raypak heat pump, adjust it so that adequate flow passes through the unit (usually 20–30 GPM minimum; see manual).
• Inspect Raypak inlet screen/strainer: Some Raypak models have an internal strainer or screen at the water inlet. With water off and pressure relieved, open the union and clean any debris.
• Test the flow/pressure switch: With power off, locate the flow or pressure switch on the Raypak water manifold. Check wiring connections for corrosion or looseness. If flow is clearly good but FLO persists, the switch may be stuck or failed and should be replaced.