Topside control panel displays OH and spa shuts down; water in the spa feels excessively hot, often above 108°F (42°C).

Safety first: Turn off power at the GFCI breaker before touching any components. Overheated water can cause burns—allow the spa to cool with the cover open.

• Step 1 – Power reset: Turn off the spa at the GFCI breaker for 5–10 minutes. Open the cover and let the water cool. Restore power and see if the OH code clears.
• Step 2 – Verify water temperature: Use an independent thermometer to compare actual water temperature to the topside display. If the display is much higher than actual, suspect a bad temperature or high-limit sensor.
• Step 3 – Check circulation and filters: Remove and rinse the Catalina filter cartridges with a hose. Run the spa with filters removed for 10–15 minutes. If OH does not return, replace clogged filters.
• Step 4 – Inspect for stuck heating: With power on and the spa at set temperature, verify that the heater indicator on the topside or control pack is not constantly on. If the heater stays on even when set temperature is reached, the heater relay on the Catalina control pack may be stuck closed and needs professional replacement.
• Step 5 – Sensor inspection: Locate the temperature and high-limit sensors threaded into the heater tube on the Catalina control pack. Check for corrosion, loose connections, or damaged wires. If resistance readings are out of spec (per Catalina service manual), replace the sensor set.

When to stop: If OH returns immediately after reset or the heater will not shut off, disconnect power and contact a qualified spa technician—continued operation is unsafe.