Richmond tankless heater shows error 13 and shuts down; may be accompanied by loud combustion noise.

Safety first: Turn OFF power and gas. Combustion problems can create carbon monoxide—do not operate the heater until the issue is resolved.

• Inspect burner: Remove the burner assembly per the service manual. Clean dust, lint, and rust from the burner surface and ports using a soft brush and vacuum.
• Check vent sizing: Compare your vent diameter, length, and number of elbows to Richmond's installation requirements. Correct any undersized or overly long vent runs.
• Clean flame sensor: As with error 12, clean the flame rod with fine abrasive pad and ensure secure wiring connections.
• Air/gas adjustment (pro only): A licensed technician should verify combustion using a combustion analyzer and adjust gas valve or air settings if your model allows.
• Board diagnosis: If mechanical and venting issues are ruled out, the control board's flame sensing circuit may be defective and require replacement.