Tankless heater shows E3 and water temperature fluctuates or unit shuts down during use.

Safety first: Turn OFF power and gas. High flue temperatures can indicate dangerous combustion conditions and risk of fire or carbon monoxide.

• Inspect exhaust vent: From the heater to the termination, check for crushed sections, bird nests, insect screens clogged with lint, or ice buildup. Clear any obstructions and ensure all joints are sealed and properly supported.
• Check vent material and length: Confirm that the vent pipe type (PVC, CPVC, polypropylene, or stainless) and total length comply with Richmond's installation manual. Excessive length or too many elbows can cause overheating; correct if needed.
• Clean heat exchanger: Mineral scale or soot can restrict flue passages. Follow Richmond's descaling procedure: isolate the heater with service valves, connect a pump and hoses, and circulate a manufacturer-approved descaling solution through the heat exchanger for the recommended time. Flush thoroughly with clean water afterward.
• Inspect exhaust temperature sensor: Locate the flue/exhaust thermistor on the heat exchanger outlet. Check wiring for damage or loose connections. If the sensor is cracked or deformed, it should be replaced.
• Test operation: Restore gas and power, reset the unit, and run hot water while monitoring for E3. If the error returns, have a technician verify combustion and vent sizing.