What does Rinnai error code 10 mean?

Code 10 means the heater detected a problem with combustion air or exhaust flow, so it shut down before it could burn unsafely. A gas burner needs the right mix of air and fuel, and the exhaust has to leave the building. If the fan cannot move enough air through the intake, the heat exchanger, and the vent, the control board stops the burner.

That is a safety response, not a defect in itself. Do not try to defeat it. The real question is what is restricting the air, and Rinnai's manual gives a clear order for finding it.

Rinnai's list, in the order a technician tends to work through it, looks like this:

• A clogged or frozen condensate line. Condensing models, the SENSEI series in Rinnai's manual, drain water that forms in the exhaust through a condensate line into a trap. If that line clogs or freezes, it backs up into the trap inside the heater and the unit shuts off to prevent spilling. Rinnai says this sets off code 10.
• A dirty inlet air filter. Rinnai puts an air filter under the front cover, in the top right of the cabinet. A filter choked with dust will starve the burner of air.
• A blocked, crushed or badly built vent. Rinnai tells technicians to inspect the whole intake and exhaust run, inside and out. They look for clearance problems, the wrong vent material, joints that are not fully seated, and pipe cut to the wrong length. Even foam sealant sprayed around the wall opening can collapse a vent pipe.
• Too much vent length. Every vent system has a maximum equivalent length, and elbows count as extra pipe. In Rinnai's concentric venting, a 90 degree elbow counts as six feet and a 45 degree elbow as three feet. Exceed the limit and the fan cannot keep up.
• Debris in the vent. Water, condensation, insects or other objects in the pipe, or a terminal too close to a wall, overhang or another vent.
• Debris in the fan, burner or heat exchanger. Rinnai says buildup between the fins of the heat exchanger restricts airflow and leads straight to code 10. A stuck check valve behind the fan housing does the same.
• Parts and settings. A defective fan motor, a damaged wiring harness, a bad control board, or altitude and vent length settings that do not match the install.

Note the installation angle: Rinnai says skipping the vent maker's lubricant when assembling joints can leave them badly sealed, which leads to exhaust leakage and code 10. That is a reminder that a new install with code 10 is often an installation issue, not a broken heater.

Start with the safety rule. If you smell gas, do not run the heater or touch switches. Leave, then call Southwest Gas at 877-860-6020 and 911 from a safe place. A code is not worth a risk.

If there is no smell, these are within reach for a homeowner:

1. 1Look outside at the vent terminals. Clear leaves, a bird nest, wasp nests, cobwebs, or anything leaned against the wall. Do not put your hand near a hot exhaust.
2. 2Check the condensate drain, if you have a condensing model. Look for a kinked hose, a hose pinched under something, or a discharge point that is plugged with debris. In a hard freeze, a condensate line outdoors can ice up, though Phoenix is milder than most places.
3. 3Power the heater off, wait a minute, and turn it on again. If code 10 does not return, watch it for a few days.
4. 4Ask when it started. Code 10 that began after a wall was patched, a shed was built near the vent, or a new appliance was added tells a technician where to look.

The inlet air filter sits behind the front cover. Rinnai's manual is written for qualified professionals, and the front panel comes off only for service. Turn off power, gas and water first. If you are not comfortable working near gas piping and electrical parts, leave the filter to the person you call. Rinnai adds that the unit should never run with its front panel off or its vent disconnected.

The usual test is smart and simple. With the heater coding out, the technician removes the exhaust vent from the top and turns on hot water to see whether the heater runs without coding. Rinnai says if it does, the restriction is in the vent, not the heater. They then reconnect the vent right away, because Rinnai warns never to leave a heater running with vent piping disconnected.

From there they mark each vent joint with a marker, separate the sections and check insertion depth. They also verify vent length and elbow count against the installation manual, examine the pipe for a collapsed section, look inside with a flashlight or camera, pull the fan to inspect the blower wheel, and clean the burner and heat exchanger fins. Rinnai says a heat exchanger with fin buildup needs to be blown out with compressed air at 120 psi, with safety glasses and a mask, or replaced if it cannot be cleaned.

### How is this different from Navien and other brands?

Other makers use similar logic with different numbers. Navien's manual, for example, has code E110 for abnormal air pressure, with two fixes: make sure the exhaust pipe is free of obstructions, and clean the intake air filter. The pattern is the same. Air in, exhaust out, filter clean, vent clear.

If your Rinnai shows a different code, see our pages on Rinnai error code 11 for no ignition and Rinnai error code 12 for flame failure. Vent trouble can cause either of those as well, since exhaust that recirculates into the intake makes a flame unstable.

Call when the vent looks fine and the code comes back, when the condensate line is clear and the heater still trips, or any time the work needs the front panel off, a gas connection opened, or a fan pulled. If the vent looks clear and code 10 keeps returning, HQ Plumbing and Air can trace it. We are licensed and insured, we answer emergency calls around the clock, and the estimate is free, with the price given before we start.

Is the heater itself at fault? Sometimes. Rinnai lists a defective fan motor, a defective wiring harness to the fan, and a bad control board as causes once the vent, filter and drain are ruled out. A technician should confirm those with a meter before any part is ordered, since the same code comes from several cheaper causes first. That order keeps you from paying for a fan you did not need.

A quick note on maintenance. Rinnai recommends flushing the heat exchanger, and in Phoenix the hard water makes that matter. Our page on descaling a tankless water heater in Phoenix gives the schedule. Scale sits inside the water passages, which is a different problem from the air fins that cause code 10, but a well kept heater has fewer faults of every kind.

If your Rinnai shows an overheat code instead, see our page on Rinnai error code 14, which covers the overheat sensor and thermal fuse.