E13 appears and the unit will not start; fan and heater remain off.

Safety first: Disconnect power. The safety chain is directly related to overheat protection; handle with care and do not bypass permanently.

• Trace safety chain: From the AC input to the heater, identify the series of safety components: thermal fuse, high-limit thermostat, and sometimes additional cutoffs.
• Check continuity: With a multimeter, test each safety device individually for continuity at room temperature. Any device that is open must be replaced with the same rating.
• Inspect connectors: Ensure all crimp and spade connectors are tight and not oxidized. Reseat any loose connectors.
• Verify wiring order: If the unit has been serviced before, confirm that the safety devices are wired in the correct series order according to the wiring diagram (if available).
• Reassemble and test: After replacing any open safety device, reassemble and test. If E13 persists, the main PCB may be misinterpreting the safety chain status and may need replacement.