Display shows HL or HOT and spa shuts down; heater icon may be off but water is very hot near the heater manifold.

Safety: Turn off power at the GFCI breaker before working on plumbing or electrical components.

• Step 1 – Verify valves are fully open: Locate the slice (gate) valves on each side of the pump and heater assembly. Ensure the handles are pulled up and locked in the open position.
• Step 2 – Bleed air from system: With power off, loosen the pump union on the discharge side slightly until you hear air escape and see a small amount of water. Retighten the union snugly (do not overtighten).
• Step 3 – Clean filter: Remove the Tuff Spas filter cartridge and rinse thoroughly. Try running the spa briefly without the filter to see if HL clears (do not leave it running long-term without a filter).
• Step 4 – Power up and test: Turn the breaker back on and monitor the display. If HL clears and does not return, the issue was likely flow-related.
• Step 5 – Sensor check: If HL persists, the high-limit sensor (usually mounted in the heater tube) may be faulty. Inspect the sensor wiring for damage or corrosion at the control pack. Replacement of the sensor is typically straightforward but must be done with power off and correct part for your Tuff Spas model.

If you are not comfortable working around water and electricity, have a spa technician replace the high-limit sensor and verify heater operation.