Spa will not heat; water stays at or near ambient temperature even though pumps run and no error code is displayed.

Safety first: Turn off power at the GFCI breaker. Verify with a non-contact voltage tester before touching any wiring. Water and electricity are a lethal combination.

• 1. Confirm demand for heat: Set the spa temperature several degrees above current water temperature and ensure the spa is not in Economy or Sleep mode.
• 2. Check for subtle codes: Some models briefly flash heater icons or small text; verify that no flow or sensor codes are present.
• 3. Feel heater tube: After 15–20 minutes of run time (with power ON), carefully feel the outside of the stainless heater tube. It should be warm if the heater is working. If it is cold, the heater is likely not energizing.
• 4. Inspect heater wiring: With power OFF, open the control box and check that the heater wires are firmly attached to the heater terminals and the control board relay.
• 5. Resistance test (for qualified persons): Disconnect heater leads and measure resistance across the heater element with a multimeter. A typical reading is 8–20 ohms depending on wattage. Infinite resistance indicates an open element.
• When to call a technician: Heater replacement involves electrical and plumbing work and should generally be performed by a spa technician, especially if the control board relay is also suspect.