Rinnai code 63: recirculation low flow

Many Rinnai models include a recirculation pump that keeps hot water moving through a loop so it arrives at the tap faster. Code 63 means the heater expected recirculation flow and did not get enough.

Rinnai makes several generations of tankless heaters (SENSEI, SENSEI RX/CX and older non-SENSEI models). The meaning below comes from Rinnai's own diagnostic code guide; the exact service steps differ slightly between generations.

What to check first

1. Make sure the cold inlet and hot outlet isolation valves under the heater are fully open.
2. Turn off the water, drain the unit and clean the inlet filter and, on crossover setups, the bypass filter.
3. Purge air from the lines by running each hot tap until the water flows smoothly with no sputtering.

Other causes Rinnai lists

• Wrong recirculation setting. The heater has to be set for the type of system installed: none, a dedicated return line or crossover. A unit set for recirculation with no pump connected will show this code.
• No power to the pump. The pump should receive 120 volts.
• A loop that is too long. Rinnai gives a maximum equivalent length of about 400 feet with 3/4-inch pipe or 100 feet with 1/2-inch pipe.
• A leak in the house plumbing. Rinnai explains that when the pump draws more water than a leak lets in, it can pull air into the system. A pressure test on the house plumbing will show it.

How to reset it

1. Close all hot water taps.
2. Turn the water heater off at the temperature controller, wait about a minute, then turn it back on.
3. Open a hot tap and watch whether the code returns.

If the same code comes back, the cause is still there. Resetting over and over is not a repair.

When to call a technician

Settings, pump testing and plumbing pressure tests are best done by the installer, especially if the code started right after a new installation or a plumbing repair.

See the full list on our Rinnai error codes page.