Tesy heater shows E18; the unit may indicate sensor overrange or underrange conditions intermittently.

Safety first: Isolate power and allow the heater to cool.

Steps:

• Wiggle test: With power OFF, gently move the NTC sensor cables along their length while watching for visible damage or stiffness indicating internal breaks.
• Clean connectors: Disconnect sensor plugs from the board and clean contacts with electrical contact cleaner. Reconnect firmly.
• Secure cables: Use cable ties to keep sensor wires away from hot surfaces and sharp edges.
• Replace suspect harness: If moving the cable previously caused E18 to appear/disappear, replace the NTC sensor harness or the entire sensor assembly.
• Test: Restore power and monitor over several heating cycles to ensure the error does not recur.