Rinnai Tankless Water Heater Flame Rod Replacement Guide

Rinnai Tankless Water Heater Flame Rod Replacement Guide — What This Part Does

The flame rod (also called the flame sensor or flame electrode) sits in the burner area and detects when combustion is active. It sends a small signal back to the control board to confirm flame presence. Without that signal, the unit will not ignite or will shut down immediately after ignition for safety. The rod fails when carbon buildup or contamination coats the electrode tip, blocking the signal. Loose mounting, corrosion, or physical damage to the rod or its wiring also prevents proper flame detection.

Over time, combustion byproducts can deposit on the rod surface. Even a thin layer of carbon insulates the electrode and stops the current flow the board needs to sense. Moisture, improper venting, or burner contamination accelerates buildup. A cracked ceramic insulator or damaged wire harness will cause the same ignition or flame-loss faults.

Jump to Replacement Steps

Signs It Needs Replacing

• Error code 11 or ignition failure The heater tries to ignite but stops with code 11, indicating no flame was detected during startup.
• Error code 12 or flame-loss shutdown The unit lights briefly then shuts off with code 12, meaning the flame signal was lost during operation.
• Burner fires but unit immediately stops You see or hear ignition for a second, then the heater cuts out and resets.
• No hot water and repeated ignition attempts The heater cycles through ignition sequences without staying lit or delivering hot water.
• Visible carbon or soot on the flame rod tip When you inspect the burner area, the rod electrode has a black or brown coating.
• Intermittent operation or random shutdowns Hot water works sometimes but the heater shuts down unpredictably, often during a hot-water call.

How to Replace It

1. Turn off electrical power to the water heater at the breaker or disconnect switch, then close the gas shutoff valve on the gas line leading to the unit.
2. Remove the front cover or access panel (typically secured by screws at the bottom and sides) to expose the burner chamber and combustion assembly.
3. Locate the flame rod assembly inside the burner box (a metal or ceramic rod with a wire lead, positioned near the burner to sit in the flame path).
4. Disconnect the wire connector from the flame rod terminal, then remove the mounting screw or bracket that holds the rod in place.
5. Pull the flame rod and gasket straight out of the mounting hole, noting the orientation and depth of the rod for reinstallation.
6. Inspect the rod tip for carbon buildup or damage (if only lightly soiled, you may clean it with fine-grit sandpaper or a non-abrasive pad, but Rinnai recommends replacement if the gasket is disturbed).
7. Install the new flame rod with a new gasket, inserting it to the same depth and angle as the original so the tip will be in the flame when the burner fires.
8. Tighten the mounting screw or bracket to secure the rod, reconnect the wire lead, and verify all connections are snug and correctly seated.
9. Reinstall the front cover, open the gas shutoff valve, restore electrical power, and initiate a hot-water call to confirm ignition and stable operation without fault codes.

The Part You Need

When to Call a Pro

If cleaning or replacing the flame rod does not clear the ignition or flame-loss fault, the problem may be low gas pressure, incorrect fuel-type configuration, venting or airflow restrictions, burner contamination, or a faulty control board. Diagnosing gas supply issues, verifying line sizing, adjusting combustion settings, and working inside the gas-valve or burner assembly require a licensed technician with proper manometers and combustion-analysis tools. Call a Rinnai-qualified service tech if you see repeated codes after rod replacement, if you smell gas, or if you are not comfortable working with gas appliances. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.