Display shows “OH” and spa shuts down; water may feel excessively hot near heater return.

Safety first: Turn off power at the GFCI breaker. Do not use the spa until the cause is identified.

• Remove cover and cool water: Open the spa cover to allow heat to escape. Let the water cool below 100°F before restarting.
• Check water flow: Ensure all jets and diverter valves are fully open. Remove and thoroughly clean the Caldera filter cartridge. Run the spa briefly with the filter removed to test flow.
• Inspect circulation: With power restored, verify that the E5 circulation pump is running and that you feel steady flow at the heater return or dedicated circulation jet.
• Check for localized overheating: If water near the heater return is much hotter than the rest of the spa, the heater may be cycling improperly or a relay may be stuck.
• Test sensors (advanced): If you have a multimeter and the service manual, you can ohm-test the high-limit thermistor at the IQ control board. A sensor reading far out of spec should be replaced.

If the “OH” code reappears immediately after reset, contact a qualified technician to inspect the heater relay and control board.