Display shows E05 and heater will not start; may appear after dry firing or air in the system.

Critical safety: A blown thermal fuse indicates dangerous overheating. Do not bypass or short any safety device. Disconnect power at the breaker before work.

• 1. Visual inspection: Remove the cover and locate the thermal fuse or one-time overheat protector on the heat exchanger. Look for discoloration or physical damage.
• 2. Continuity test: With power off, disconnect one lead and measure continuity across the thermal fuse or safety thermostat. If open circuit and it is a non-resettable fuse, it must be replaced.
• 3. Investigate cause: Determine why the unit overheated (no water flow, air lock, failed control board, scaled heat exchanger). Correct the underlying issue before replacing the fuse.
• 4. Replace protection device: Install an identical Kospel-specified thermal fuse or safety thermostat. Ensure firm contact with the heat exchanger surface and proper insulation where required.
• 5. Wiring check: Inspect the overheat protection wiring harness for burns or loose connections and repair as needed.

Because this involves critical safety components, replacement is best performed by an authorized Kospel technician.