Tesy heater shows E15; overheat protection has been triggered repeatedly.

Safety first: Allow the heater to cool completely. Turn off power at the breaker before removing covers or pressing any reset buttons.

Steps:

• Reset safety thermostat: Locate the manual reset safety thermostat (often a red button on the thermostat housing or element flange). Press firmly until a click is felt.
• Check for scale: If trips are frequent, drain the tank and inspect the element for heavy limescale. Descale or replace the heating element assembly.
• Verify sensor placement: Ensure the main NTC sensor and safety thermostat are properly clamped or inserted into their wells for accurate temperature sensing.
• Check control logic: If the element remains energized even when the set temperature is reached, the control board or thermostat relay may be stuck and must be replaced.
• Test after reset: Refill (if drained), restore power, and monitor a full heating cycle. If E15 or trips recur, stop using the heater and have a technician inspect it.

Warning: Repeatedly resetting an overheating heater without fixing the cause is dangerous and can damage the tank or cause scalding.