Spa powers on but will not heat; temperature stays well below set point even after many hours.

Safety: Turn off power at the breaker before testing or replacing heater components.

• Step 1 – Confirm mode and set point: Ensure the spa is in Standard mode and the set temperature is higher than current water temperature.
• Step 2 – Check for flow errors: If FLO or similar codes appear, resolve those first; the heater will not run without proper flow.
• Step 3 – Feel heater tube: After running for 15–20 minutes (with power on), carefully feel the metal heater tube. It should be warm if heating. If it is cold, the heater is likely not energizing.
• Step 4 – Electrical testing: With power off, a technician can test heater element resistance at the terminals and verify correct voltage when the heater should be on.

Heater replacement on a Tuff Spas unit involves draining below the heater, removing unions, and wiring the new heater to the control pack. This is best done by a qualified spa technician.