Display shows OH or OHH and spa shuts down; water may feel excessively hot near heater area.

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

• Remove spa cover: Allow the spa to cool with the cover off. Verify actual water temperature with a separate thermometer.
• Check for pump operation: With power restored, ensure the primary pump and/or circulation pump runs when heating is called for. Weak or no flow can cause localized overheating.
• Inspect filter and valves: Clean or replace the Coast Spas filter cartridge. Confirm all slice valves are fully open and no jets are closed off in the heater return path.
• Test temperature sensor: If the displayed temperature is clearly inaccurate compared to a thermometer, the temp sensor may be faulty and should be replaced.
• Heater relay check (advanced): If the heater indicator is on even when the spa is at or above set temperature, the heater relay on the control board may be stuck closed. This requires control pack or board repair/replacement by a qualified technician.