A. O. Smith Tankless Reset: Where It Is and When to Use It
On this page (6 sections)
The Short Answer: A. O. Smith gas tankless heaters do not have a red reset button like a tank heater. A lockout is cleared by switching the heater’s power off at its switch, plug, or breaker, waiting several seconds, and switching it back on. That only helps once the cause is fixed. Note the error code first, because the code tells you whether a reset is reasonable or the heater needs service.
Why there is no reset button
On a tank-type heater, the red button is a mechanical high-limit switch. A tankless heater’s safety logic lives on its computer board instead: when it detects a problem it stops firing and shows a code, and the code stays until power is interrupted. Some models also have internal safety devices (such as a high-limit switch on the heat exchanger) that the technician checks, but these are not owner reset points.
Read the code before you reset
Depending on the model, the code shows on the remote controller, as a number on the board’s display, or as a number of blinks of a red LED on the board (on the 110 and 310 models). The table lists the codes A. O. Smith publishes for its 110, 310 and 510 models in the owner’s guide (opens in a new tab). Other A. O. Smith tankless lines use their own tables; check the manual for your model number.
| Code (remote) | Red LED blinks (110/310) | A. O. Smith’s description | Is a reset reasonable? |
|---|---|---|---|
| 10 | 5 | Warning that leads to code 99 | Only after checking the vent; see below |
| 11 | 3 | Ignition failure | Once, after confirming gas is on |
| 12 | 3 | Loss of flame | Once, after confirming gas is on |
| 31 / 32 | 2 | Outlet / inlet temperature sensor failure | Once; service if it returns |
| 61 | 4 | Fan motor fault | No; service |
| 72 | 6 | False flame detection | No; service |
| 99 | 5 | Imperfect combustion | No; service |
Code 10 and code 99 both point to combustion problems. A. O. Smith’s checks include blocked intake or exhaust, the wrong gas type, altitude, and grease or dirt in the burner and fan. Those are not things a reset fixes.
How to reset safely
- Record the code, the time, and what was happening (first use of the morning, during a storm, right after a gas meter change).
- Fix what you can see. Confirm the gas supply valve to the heater is open and other gas appliances work. On outdoor models, and on indoor models with wall terminations, look for snow, leaves, or nests at the vent. If you use propane, check the tank is not empty.
- Cycle power. Turn off the heater’s switch or unplug it, or turn off its breaker. Wait several seconds (longer if your manual says so), then turn it back on.
- Try one hot tap. If hot water returns and no code reappears, keep an eye on it. If the same code comes back, stop resetting.
The temperature buttons on the remote controller change settings; they do not clear a lockout.
When a reset is the wrong answer
- The code comes back on the next use. The cause is still there. Repeated ignition attempts with a gas or venting problem are unsafe, and they wear the igniter.
- You hear a bang on ignition. That is delayed ignition. Turn the heater off at the switch and call for service.
- The heater needs a reset every morning. Something happens overnight: a freezing vent, a propane regulator icing, a power interruption. Tell the technician the pattern.
- There is water dripping from the unit. A. O. Smith lists heat exchanger leaks among the checks for several codes. Turn off the heater and the water supply.
What the technician will check
For ignition and flame-loss codes, the technician checks gas supply pressure while the heater runs, the igniter and flame rod (looking for soot), wiring connections, and the high-limit switch. For combustion codes, they inspect the burner, fan, intake and vent for blockage and confirm the heater is set up for the correct gas type and altitude. Sensor codes usually come down to a damaged wire, a loose connector, or a failed thermistor. Our guide to A. O. Smith tankless with no hot water covers heaters that show no code at all, and resetting a Takagi tankless covers the closely related Takagi models.
Frequently Asked Questions
Q: My A. O. Smith tankless shows no code and still won’t heat. Will a reset help? A: Possibly, if the heater lost power or locked up during an outage. If it does not respond after one power cycle, check that water flow is high enough to start it and that the gas supply is on, then call for service.
Q: Why does my heater show code 11 after the gas company worked on the meter? A: Air can enter the gas line during meter or line work, and the first ignition attempts may fail. One reset is reasonable. If code 11 continues, have a gas technician check the supply rather than resetting repeatedly or loosening any fittings.
Q: Is it bad to reset the heater many times? A: Yes. Each failed ignition cycle adds wear, and if the cause is combustion-related, repeated attempts can be dangerous. One reset after fixing a visible cause is the limit.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith on-demand water heater installation manual and owner's guide: 110, 310 and 510 models (opens in a new tab)A. O. Smith 110 (T-KJr2), 310 (T-K4) and 510 (T-D2) gas tankless models, indoor and outdoor.
- A. O. Smith: model and manual lookup (opens in a new tab)Find the instructions for the model on your rating plate; this directory does not verify a particular error-code meaning.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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