E05 displayed, unit shuts down or will not start; may occur after overheating or poor circulation.

Warning: Water and internal components can be extremely hot. Allow the heater to cool and shut off power before servicing.

• 1. Check system pressure and air: Verify the system pressure on the gauge is within Triangle Tube specifications. Bleed air from high points and air vents. Air-bound systems can cause localized overheating.
• 2. Verify circulator operation: During a call for heat, feel the piping on both sides of the internal or external circulator pump. Both sides should get warm. If the pump is hot but no flow is felt, the circulator may be seized or air-locked.
• 3. Inspect strainers and valves: Check any system strainers or isolation valves near the water heater. A closed valve or clogged strainer can stop flow and trip the high limit.
• 4. Check high limit sensor connection: Locate the high limit temperature sensor on the supply outlet or heat exchanger. Ensure it is firmly attached and the wiring harness is secure and undamaged.
• 5. Reset and monitor: After restoring flow and bleeding air, reset the lockout from the control panel. Monitor the supply temperature. If it rises rapidly to the limit and trips again, the heat exchanger may be restricted or the sensor defective.
• 6. Professional descaling or sensor replacement: If the primary heat exchanger is scaled or partially blocked, it should be chemically cleaned or replaced by a qualified Triangle Tube technician. High limit sensor replacement also requires proper sealing and testing.