Tesy water heater shows E02 and stops heating; sometimes trips safety thermostat.

Safety first: Turn off power at the breaker and verify with a multimeter. Allow the heater to cool; hot water and metal surfaces can cause burns.

Diagnostic and fix steps:

• Power reset: After cooling, switch the breaker OFF for 2–3 minutes, then ON. If E02 reappears immediately, continue with checks.
• Inspect sensor and wiring: Remove the front or bottom cover. Locate the NTC sensor wiring from the tank to the control board. Check for damaged insulation, signs of water leakage, or condensation around the sensor pocket.
• Measure NTC resistance: Disconnect the sensor from the board and measure resistance. A reading close to 0 Ω indicates a shorted sensor. Replace if shorted or if resistance is far outside the expected range for room temperature.
• Check for moisture: If there is water or moisture around the sensor well, dry the area thoroughly and inspect for tank seepage. A leaking sensor well gasket must be replaced.
• Replace faulty parts: Install a new Tesy NTC temperature sensor and new sensor well gasket if needed. Reconnect wiring securely.
• Test operation: Restore power and monitor the temperature rise. Ensure E02 does not return and that the safety thermostat does not trip.

Call a professional: If the sensor and wiring are good but E02 persists, the control board may be defective and should be tested or replaced by a qualified technician.