Display shows E2 and water temperature is unstable or unit shuts down shortly after starting

Safety first: Disconnect electrical power and allow the water heater to cool. Hot water lines and fittings may be very hot.

Steps to check:

• Locate the outlet water temperature sensor (outlet thermistor) on the hot water outlet manifold of the CTC heater.
• Inspect the sensor body for cracks or mineral buildup that may have stressed the sensor. Clean light scale with a non-metallic brush if needed.
• Check the wiring harness from the outlet thermistor to the main control PCB. Ensure connectors are fully seated and not corroded.
• Test the thermistor resistance with a multimeter and compare to the CTC specification chart. Replace the outlet thermistor if readings are out of range.
• If the sensor and wiring are good but E2 persists, the temperature sensing circuit on the main control PCB may be defective and require replacement.

Tip: Replace both inlet and outlet thermistors at the same time if the unit is older and you are already accessing the plumbing manifold.