Display shows OH or OHH, spa shuts down all functions, water is very hot (often above 108°F).

Safety first: Turn off power at the GFCI breaker immediately. Do not enter the spa if water is excessively hot.

• 1. Remove cover and cool water: Open the Coleman spa cover fully and allow the water to cool naturally. You can add some cool water to speed the process, but do not drain while very hot.
• 2. Check for pump operation: Once cooled below 100°F, restore power and observe whether the circulation pump runs and whether the heater indicator on the topside panel behaves normally (turns off when set temperature is reached).
• 3. Inspect temperature sensor: Locate the temperature sensor (thermistor) threaded into the heater tube or inserted in a dry well. Ensure it is fully seated and not hanging loose. Check for damaged or corroded wiring.
• 4. Compare displayed temperature: Use a reliable thermometer in the spa water. If the displayed temperature is significantly different (more than 3–4°F), the sensor may be faulty and should be replaced.
• 5. Suspect stuck heater relay: If the heater continues to heat even when the set temperature is reached or when the spa is in standby, the heater relay on the Coleman control board may be stuck closed. This is a serious fault and requires control board replacement by a qualified technician.
• 6. Environmental factors: In hot climates, reduce filtration/heating cycles during the hottest part of the day and leave the cover slightly vented to prevent overheat.