What does Rinnai error code 63 mean?

Rinnai titles code 63 Recirculation Low Flow, and lists it for both the SENSEI series and the older non-SENSEI models. It only applies to heaters set up for recirculation, meaning the pump logic is turned on and the heater expects a loop of water to return to it. The idea of recirculation is simple: instead of waiting for cold water in the pipes to run out at a faucet, a pump keeps hot water moving so it is near the fixture when you open the tap. If that pump cannot move enough water, the heater flags it.

### How does Rinnai's recirculation work?

Rinnai's manual describes two modes. Dedicated mode is the factory default, for a home that has a dedicated return line in the plumbing. Crossover mode is for a home without a return line and uses a thermal bypass valve at the farthest fixture, connecting the hot and cold lines so that water can circulate. The manual says the setting called parameter 04 has to match the mode in use. Rinnai's diagnostic steps repeat this point more than once, so a wrong mode setting is a known cause of code 63.

The installation manual adds that a fixed recirculation schedule needs an optional timer or Wi-Fi controller, and that without one the heater can start the pump temporarily if power to the appliance is reset. Those are technician-set features, but they explain why a heater may run its pump at times you do not expect.

Rinnai's diagnostic manual lists fourteen steps. In owner terms they fall into a few groups.

The valves, the filters and the air

• Clear the filters of debris, reinstall them and bleed the plumbing system of air.
• Make sure the cold water inlet and hot water outlet valves are open.
• Purge air from the recirculation line by running water until no air can be heard at the fixtures.
• Open the bleeder valve installed below the water heater and let the air out.

The pump and the loop

• Make sure the recirculation pump is getting the proper supply voltage at its wiring, which Rinnai gives as 120 VAC.
• On a dedicated return, make sure the line does not exceed the maximum length allowed for its pipe size, and that the comfort or economy setting is correct.
• With the water supply off, in dedicated mode, make sure the plug was installed in the filter housing on the recirculation side of the heater.
• In crossover mode, make sure the bypass plug is removed and the bypass filter is installed.

The settings

• Confirm the DIP switches on a non-SENSEI model match the recirculation type, crossover or dedicated.
• On a SENSEI model, confirm parameter 04 is correct: A means no recirculation, B means dedicated recirculation, C means crossover with a long loop and D means crossover with a short loop. Parameter 05 chooses economy or comfort mode.
• If a SENSEI model has no circulation pump connected at all, parameter 04 has to be A. Rinnai says a heater set to B with no pump will code out with 63.

The building plumbing

• Rinnai describes a test for a hidden leak. The technician isolates the home's loop and runs a hose between the hot and cold connections to make a small loop of the heater's own. If the heater runs without throwing a code 63, the problem is air or a leak in the home's plumbing. The technician then pressurizes a gauge at an outdoor hose connection, shuts off the main water feed and watches whether pressure bleeds down.

### Why would a leak cause a low flow code?

Rinnai gives the reason directly. When the circulation pump comes on, it draws a higher flow rate than the leak. That pulls air into the system, and air in the loop cuts the flow the heater measures. In other words, a code 63 that keeps returning can be the first sign of a small leak somewhere in the plumbing that is too small to see. That makes it worth taking seriously, especially in a slab home where pipes are out of sight. Our page on the signs of a slab leak in Arizona covers what to watch for.

As with any gas appliance, the first rule is the gas smell rule. Should you smell gas, leave the building before you do anything else, and make the call to Southwest Gas at 877-860-6020 or 911 from outside.

With no smell, safe owner checks are limited to a few things:

• Look at the shutoff valves. Rinnai's list includes making sure the hot and cold valves at the heater are open. A valve that is not fully open restricts the flow the pump can draw.
• Try turning the power off, waiting, and turning it back on. For the temperature controller, Rinnai's owner manual describes power resets for several codes. Note that the manual does not give a specific reset step for code 63.
• Run a hot tap for a minute and listen. Rinnai describes purging air until none can be heard at the fixtures. If you still hear air at the fixtures, tell the technician, because air that returns is one of the things Rinnai's steps are trying to track down.
• Note when it happens. If the code appears after work on the plumbing, a water shutoff or a pump replacement, tell the technician.

The inlet filter and the bleeder valve involve draining or opening a pressurized water line. Rinnai's manual cautions that the system is pressurized and to have a bucket ready, and that the water supply be turned off before removing filters. Unless you have done it before, leave that to a plumber.

### Does a home need recirculation at all?

Not every home does, and that is part of why code 63 can surprise people. A house with a recirculation loop, or a heater set up with a thermal bypass valve at the farthest fixture, depends on the pump. A house with neither does not. If you do not know whether yours has one, ask whoever installed it. Rinnai's diagnostic manual says a SENSEI model set for dedicated recirculation with no pump connected will code out with 63. That can happen after a settings change, a replacement circuit board or a service visit, so tell the technician what has been done to the heater recently. Our page on whether a recirculation pump is worth it explains how the systems work, and why a recirculating pump can heat your cold lines covers a common side effect of crossover systems.

Call if code 63 returns after you have checked the valves, if the pump has no power or will not run, if you suspect air keeps entering the loop, or if water bills or wet spots suggest a leak. A recirculation loop that draws air is also a loop that can be losing water.

HQ Plumbing and Air is licensed and insured, and we answer emergency calls 24/7. Free estimates and upfront pricing come standard. For all the other codes, see our Rinnai tankless code list. If the trouble is a long wait for hot water and not a code, our page on instant hot water at every faucet explains the options.