Control panel displays OH and spa shuts down; water feels extremely hot or above set temperature.

Safety first: Turn off power at the GFCI breaker before touching any components. Extremely hot water can cause burns—do not enter the tub until temperature is safe.

• Step 1 – Power reset: Turn off the spa at the GFCI breaker for 5–10 minutes, then restore power. See if the OH code clears after the system reboots.
• Step 2 – Verify actual water temperature: Use an independent thermometer in the spa water. If the displayed temperature is much higher than actual, suspect a bad temperature sensor or high-limit sensor on the Nordic control pack.
• Step 3 – Check water level and flow: Ensure water level is above all jets and suction fittings. Open all slice valves. Remove and clean the Nordic filter cartridge; a clogged filter can cause low flow and localized heater overheating.
• Step 4 – Inspect circulation: With power on and OH cleared, verify that the circulation pump (if equipped) or primary pump is running when heat is called. Weak or no flow through the heater tube can cause OH trips.
• Step 5 – Examine heater and sensors: With power off, inspect the heater tube on the Balboa/Nordic control pack for two sensors (temperature and high-limit). Check for corrosion, loose sensor clips, or damaged wiring. Reseat sensor plugs on the control board.
• Step 6 – Suspect stuck heater relay: If the heater indicator on the topside is off but the heater still warms the water, the heater relay on the control board may be welded closed. This requires control board replacement by a qualified technician.

Do not bypass safety sensors. If OH returns repeatedly, discontinue use and have the spa inspected.