Rinnai Non-SENSEI Code 63
Recirculation low flow. The recirculation circuit is not moving enough water. On this generation the first thing Rinnai checks is a hardware setting — the switches on the PC board have to match the type of recirculation system installed, crossover or dedicated — where the SENSEI generations use a software parameter instead. After that it is the same list: the bypass plug and filter fitted correctly for the mode, filters clear, air bled out of the loop, isolation valves open, and 120 VAC at the pump. The RH180 hybrid has its own version of this code, written around a circulation flow rate below 1.3 GPM, and it is not what is described here — that one has its own page.
DIY fixThe verdict
No parts needed — reset or re-check a setting
Frequently air in the loop or a clogged filter, and both are yours. Nothing has failed on the heater itself in the common case — but if the system was recently reconfigured, the setting on the board is a professional adjustment.
Typical cost: $0–$600
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Non-SENSEI — not averaged across the brand.
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 53), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Confirm the cold inlet and hot outlet isolation valves are both fully open.
- Clean the inlet water filter — a clogged filter starves the loop and is the cheapest thing on this list.
- Bleed air out of the recirculation line: run hot fixtures until you cannot hear air at them.
- Check the recirculation pump has power.
- If the recirculation system was recently changed or added, book a service call — the board setting has to match the system type and that is not a homeowner adjustment.
Code 63 on other Rinnai series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: