Tesy water heater shows E13; unit may shut down with no obvious temperature issue.

Safety first: This fault may indicate a shock hazard. Switch off power at the breaker and do not operate the heater until the fault is located and corrected.

Steps:

• Visual inspection: Check the power cable, terminal block, and internal wiring for signs of burning, cracking, or moisture.
• Insulation test of element: With all wires disconnected from the heating element, use a megohmmeter (insulation tester) between each element terminal and earth. Values should typically be >1 MΩ. Low resistance indicates leakage and the element must be replaced.
• Check for water leaks: Inspect around the element flange and sensor wells for leaks that could wet electrical parts. Repair leaks and dry thoroughly.
• RCD / GFCI check: Ensure the external RCD/GFCI (if present) is functioning correctly and not nuisance-tripping due to wiring issues.
• Replace faulty parts: Replace the heating element assembly or any damaged wiring. If the internal detection circuit is faulty, replace the control board.

Warning: Earth leakage testing should be performed by a qualified electrician or technician.