F18 appears; heater shuts down during operation, often on very hot days.

Safety first: Turn off power and allow the heater to cool before inspection.

• Check clearances: Ensure the heater has the required clearance from walls, fences, and other equipment. Do not store items against the cabinet.
• Clean louvers and screens: Remove debris, leaves, and cobwebs from all air intake and exhaust openings on the cabinet.
• Inspect cabinet sensor: Locate the internal temperature sensor (often clipped to the cabinet or near the control board). Check for secure mounting and wiring.
• Ambient conditions: If the heater is in a small, enclosed equipment room, improve ventilation or add an exhaust fan to reduce heat buildup.