AO Smith Tankless Reset Button
The Short Answer: Most AO Smith ATI, 240, 340, and 540 tankless units reset by killing 120-volt power for 10–30 seconds — switch, then breaker if needed — not by holding a hidden red ECO. Photograph the code first. One reset after you clear a vent, filter, or GFCI. Do not reset a 13 or a gas smell.
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Search Intent & The Real Problem
The shower died. A neighbor said “hit the reset.” You cannot find a button like a ProLine tank ECO. Lockouts live in the PCB. Power-cycling clears a latch so the unit can try again. It does not fix a blocked vent, a 1/2” gas whip, or scale. Ten resets in a morning glaze the igniter. Full no-heat tree: AO Smith tankless no hot water. Same digits on the Takagi twin: Takagi reset.
What other guides get wrong
They draw a tank-style red ECO on an ATI jacket. Many of these units have no customer high-limit button on the front. They treat reset as the repair. Reset is the last step, not the first. And they mix a Voltex hybrid Edr with a 540 tankless 16. Wrong machine, wrong button.
Step-by-Step Troubleshooting
Step 1: Capture the code before you kill power
| Code | Reset after you… | Reset at all? |
|---|---|---|
| 10 | Clear termination, condensate, bird screen | Once |
| 11 / 12 | Confirm cock open, inlet screen, no wind in the burner | Once |
| 14 / 16 | Scale / low flow — do not keep firing | After a proper flush or a tech |
| 13 | Shut gas, leave | No — licensed |
| 31 / 32 | Reseat the thermistor plug | Once to prove the wire |
| None, just dead | GFCI / disconnect | Once if power was the issue |
| Propane / NG smell | Leave | No |
- What to look for: Two-digit code on the remote or PCB LED. Photograph it and the rating plate (ATI vs 540). Reset first and you donated the only diagnostic the board had.
- Required tools: Phone camera.
Codes that keep returning are diagnosis, not a ritual — keep resetting.
Step 2: Fix the obvious cause — then reset once
- What to look for: Isolation handles parallel to the pipe. Inlet screen rinsed. Outdoor termination not nested or snowed in. Condensing 540 trap not full. Appliance gas cock open (handle parallel). Other gas appliances lighting. A packed screen looks like “needs a reset” every morning.
- Required tools: Flashlight on the vent and the cold-side filter. Bucket.
If you have no isolation valves, that is an incomplete install. Hire the flush. Do not dump acid into the house cold.
Step 3: The actual reset — power, not a paperclip
- What to look for: Appliance switch off, wait 10–30 seconds, on. If the switch does nothing, the 120-volt disconnect or GFCI. Some remotes have a function that returns to factory temperature — that is not a lockout reset. There is often no red button on the gas valve either; that is a tank Honeywell habit — Honeywell reset.
- Required tools: Your hand. No paperclip in the PCB.
Wait a full 30 seconds on stubborn latches. Five seconds is a flicker, not a reset.
Step 4: What a good reset looks like
- What to look for: Display returns, no code, unit fires on a hot-water call within the trial window, stable flame, no bang. A bang is delayed ignition — shut it down. Do not purge the gas line yourself.
- Required tools: One hot faucet, ears.
Fan must spin before spark. A silent combustion fan is carbon monoxide if anything burns. Do not keep resetting a mute cabinet.
Step 5: When the same code returns in one shower
- What to look for: Same 10 on the next hot call. Same 11 as soon as flow starts. The cause is still there. A second reset is not a procedure. A third is how you buy an igniter, a high-limit, and a heat exchanger. Outdoor unit that throws a 10 only in weather: after rain.
- Required tools: None. Call a licensed tech with the photo of the code.
Repeating 14/16 after a recent flush is a restricted exchanger, not a “reset schedule.”
When DIY Ends: Calling a Licensed Pro
Stop at code 13, gas smell, water on the board, a silent fan, repeated 11/12 after a clean filter, and any 16 that returns after a flush. You may power-cycle once and clean the inlet screen. Combustion, gas pressure, and board replacement are licensed. AO Smith / Takagi will not honor an exchanger that was reset through overheat all weekend.
Frequently Asked Questions
Q: Where is the reset button on an AO Smith tankless water heater? A: Often there is not a tank-style red ECO. Soft reset is the appliance switch or breaker off for 10–30 seconds. Photograph the code first.
Q: How do I reset an AO Smith ATI after code 11? A: Confirm the gas cock and inlet screen, then one power cycle. Failed ignition trials lock it out. If 11 returns on the next shower, hire a licensed tech.
Q: Why does my AO Smith tankless need a reset every morning? A: The cause is still present: vent, gas, scale, a packed screen, or a GFCI that weeps overnight. Daily resets are a missed diagnosis, not maintenance.