Heater shows E15 and shuts down during operation.

Safety: Turn off power and pump, and allow the heater to cool. Close isolation valves before opening any water connections.

• Check water chemistry and scaling risk: Poor water balance can cause scale that affects the internal bypass and thermal regulator.
• Inspect internal bypass and thermal regulator: Remove the header cover per Pentair instructions. Locate the thermal regulator and bypass assembly. Check for broken springs, stuck plungers, or heavy scale.
• Clean or replace components: Descale lightly with a descaling solution if minor buildup is present. Replace the thermal regulator or bypass assembly if parts are warped, cracked, or seized.
• Reassemble and test: Reinstall components with new gaskets/O-rings as needed, restore flow and power, and monitor heater operation for stable temperatures.