A. O. Smith Blinking White Light: Reading the Pattern
On this page (6 sections)
The Short Answer: A white or pale status light on an A. O. Smith gas control usually reports normal operation. A single slow flash means the heater is idle or the pilot is lit; a bright-dim “heartbeat” means it is heating. A steady light, no light, or a counted pattern with a three-second pause means something else, depending on whether you have a standing-pilot or Ultra Low NOx model.
Two kinds of A. O. Smith gas control
Look at the heater before reading the light:
- Standing-pilot models have a pilot you light with a push-button igniter and no power cord. The status light is powered by the pilot’s thermopile.
- Ultra Low NOx models plug into an outlet, have a motorized damper on top of the flue, and have a separate small control box called the LDO module with its own light. They light automatically; A. O. Smith’s guide says not to try to light the pilot by hand.
The same blink can mean different things on the two types.
Light patterns that are not faults
| What you see | Standing-pilot models | Ultra Low NOx models |
|---|---|---|
| One short flash every few seconds | Pilot lit, control normal (heartbeat) | Idle: no call for heat, no faults (once every four seconds) |
| Bright-dim pulsing heartbeat | Normal operation | Heating: call for heat, no faults |
| Steady light, not blinking | Pilot recently went out and the thermopile is cooling | Briefly after the control is switched off |
| No light | Control off or pilot out | Lockout: check the light on the LDO module |
Anything else, a count of flashes followed by a three-second pause, is a fault code. A. O. Smith’s meanings for standing-pilot models are in our blinking green light guide, and three-flash patterns are covered in A. O. Smith blinks 3 times.
Standing-pilot models: steady or no light
According to A. O. Smith’s service handbook for its FVIR gas models (opens in a new tab), a steady light means the pilot went out recently and the thermopile is cooling. The control will not let you relight until 10 minutes have passed. Turn the knob to OFF, wait the full 10 minutes, then follow the lighting instructions on the heater’s label.
After relighting, the light can take up to 90 seconds of continuous pilot operation to start blinking. If the pilot will not stay lit after a correct attempt, A. O. Smith’s technician checks include a tripped thermal switch, flammable vapors near the heater, inadequate combustion air or draft, and a clogged air filter or flame arrestor. See why a gas water heater won’t stay lit.
Ultra Low NOx models: no light on the gas control
On these models, no light on the gas control means it is locked out, and A. O. Smith’s use and care guide (opens in a new tab) directs you to the LDO module’s light:
| LDO module light | Meaning | A. O. Smith’s action |
|---|---|---|
| Heartbeat every 1 second | Normal | None |
| Flash every 1 second, gas control dark | Lint build-up detected | Remove lint and dust; check gas supply pressure; cycle power to clear |
| Flash every 4 seconds, gas control dark | Burner failure or chamber sensor failure | Technician: burner or sensor replacement |
The lint code is the one owners can often prevent. These heaters have a removable air filter around the base. A. O. Smith asks owners to inspect it at least once a year and, if it is dirty, turn off the heater, let it cool for 10 minutes, and vacuum the filter (or wash it in soap and water if oily, then dry it). A clogged filter can trigger the lint fault.
What the technician will check
For a standing-pilot heater whose light will not start blinking, the technician checks the pilot flame, thermopile output and wiring, the thermal switch, and the flame arrestor under the burner. For an Ultra Low NOx heater, they read both lights, check the damper opens and closes, check gas supply pressure, and clean the combustion chamber or replace the burner or chamber sensor as the code requires.
Frequently Asked Questions
Q: My light changed from a slow flash to a fast pulse. Is something wrong? A: Probably not. On Ultra Low NOx models the slow flash is idle and the bright-dim pulse is heating, so the light changes whenever someone uses hot water.
Q: Why won’t my standing-pilot heater relight right away? A: A. O. Smith’s control has built-in circuitry that requires a 10-minute wait between lighting attempts while the thermopile cools. Trying earlier will not work.
Q: Can the LDO module’s reset button clear a lint fault? A: A. O. Smith says the lint fault clears by cycling main power after the lint is removed. The module’s reset button is listed for the burner failure code, which needs a technician.
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 use and care guide 100283020: residential atmospheric Ultra Low NOx gas water heater (opens in a new tab)A. O. Smith residential atmospheric Ultra Low NOx gas models with electronic gas control, flue damper and LDO module.
- A. O. Smith service handbook 327726: residential FVIR gas water heaters (opens in a new tab)A. O. Smith GCV, GCVH, GVR, GCVL, GVRL, GCVT and related series 300/301 standing-pilot gas models.
- 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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