What does error code 63 mean on a Rinnai tankless water heater?

Recirculation low flow. Flow in the recirculation loop is too low.

Can I fix Rinnai code 63 myself?

Start with these safe checks: Make sure the cold water inlet and hot water outlet valves are open. Check that the recirculation pump has power. Filter cleaning and air purging involve draining a pressurized system. Have a plumber or Rinnai pro do it.

When should I call a technician for code 63?

Filter cleaning and air purging involve draining a pressurized system. Have a plumber or Rinnai pro do it. Smell gas? Leave right away, don't touch light switches or phones inside, and call your gas utility or 911 from outside. Never open a gas valve, burner, gas line, vent or flue connection, or bypass a safety switch. Repeated lockouts, scorching, soot, or a CO alarm mean shut it off and call a licensed gas technician.

Rinnai Tankless Water Heater Error Code 63: Recirculation low flow

What 63 means

Flow in the recirculation loop is too low.

Likely causes

Air in the recirculation line
Clogged inlet or bypass filter
Closed valves
Pump not powered

Safe first checks

Make sure the cold water inlet and hot water outlet valves are open.
Check that the recirculation pump has power.

When to stop

Filter cleaning and air purging involve draining a pressurized system. Have a plumber or Rinnai pro do it.

Checked against: Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652). Codes can differ by model and year, so confirm with your owner's manual.