Sime water heater shows E03 and shuts down; fan may start but burner does not ignite.

Safety: Turn off power and gas. A flue fault can lead to dangerous exhaust gas accumulation. Do not operate the heater until the issue is resolved.

Steps:

• Check outside flue terminal: Inspect the Sime concentric flue terminal for obstructions (bird nests, leaves, snow, ice). Clear any blockage carefully.
• Inspect air intake path: Ensure the air intake grill or concentric flue ring is not blocked by dirt or objects.
• Check flue gas thermostat (if accessible): Some Sime models have a manual reset flue thermostat on the top of the combustion chamber. With power off, press the small reset button if present. If it trips repeatedly, there is an underlying overheating or flue blockage issue.
• Examine fan and pressure switch tubing: Remove the front cover and inspect silicone tubes between the fan and air pressure switch. Ensure they are not kinked, cracked, or filled with condensate. Re-seat them firmly.
• Clean primary heat exchanger: If you see heavy soot or scale on the heat exchanger fins, it can cause high flue temperatures. Light brushing and vacuuming can help, but deep descaling should be done by a technician.

Call a professional: If E03 persists after clearing the flue terminal and checking tubing, a faulty flue thermostat, fan, or pressure switch may need replacement and combustion analysis by a certified Sime technician.