Display shows EC or ECO, and the spa does not heat continuously; the temperature drops between filter cycles.

Safety first: No internal work is required; this is typically a settings issue.

Change heating mode:

• Access mode settings: On the topside control, press the MODE or TEMP button (often with LIGHT or JETS) to cycle through modes until you see STD or READY instead of EC/ECO.
• Verify set temperature: Ensure the set temperature is at your desired level (e.g., 100–104°F).
• Allow time to heat: After switching to standard mode, the spa may take several hours to reach the new set temperature.