Jacuzzi pool heater will not start; display shows F1 shortly after a call for heat.

Safety first: Turn off power at the breaker and shut off the gas supply before opening the heater cabinet. Allow the heater to cool completely.

Steps to check and correct F1:

• Verify water flow: Ensure the pool pump is running at normal speed. Check that skimmer and pump baskets are clean and that all suction and return valves are fully open.
• Clean the filter: If filter pressure is high, backwash or clean the cartridge/DE filter to restore proper flow.
• Inspect the water pressure switch: Locate the water pressure switch on the water manifold of the Jacuzzi heater. Confirm the wiring is firmly connected and not corroded. With power off, remove the switch and check for debris in the port; clean gently if needed.
• Adjust the switch (if adjustable type): Some Jacuzzi pressure switches have an adjustment screw. With the pump running and heater calling for heat, a qualified person can slightly adjust the screw so the switch closes at normal system pressure. Do not over-adjust; if adjustment does not restore operation, replace the switch.
• Replace if defective: If continuity does not change with pump on/off, the pressure switch is likely failed and should be replaced with a compatible Jacuzzi water pressure switch.

If F1 persists after restoring proper flow and checking the switch, contact a qualified pool heater technician to verify hydraulic design and internal manifold condition.