Display shows H1; spa may continue to run but with limited heating control.

Safety first: Unplug the spa before touching the heater assembly.

• Check sensor mounting: Ensure the H1‑related sensor is firmly clamped to the heater tube or housing. Tighten the clamp if loose.
• Refresh thermal contact: If accessible, remove the sensor, clean the contact area, and apply a thin layer of high‑temperature thermal paste before remounting.
• Clean connector: Disconnect and reconnect the sensor plug several times to wipe oxidation from the contacts.
• Monitor readings: After reassembly, compare displayed temperature to an external thermometer over several hours. If drift remains large, replace the MSPA NTC sensor.