A. O. Smith Water Heater Humming Noise
On this page (6 sections)
The Short Answer: A steady hum from an A. O. Smith water heater is usually a motor at work: the compressor and fan on a hybrid heat pump, the blower on a power-vent model, or the damper motor on an Ultra Low NOx model. On an electric tank, a hum while heating is often a vibrating element. Grinding, a hum with no heat, or a buzz with a burning smell needs a technician.
Start with what kind of heater you have
The same word, “humming,” describes very different sounds depending on the heater:
| Heater type | What hums | Normal? |
|---|---|---|
| Hybrid heat pump (Voltex and similar), unit on top of the tank | Compressor and fan, like a refrigerator or dehumidifier | Yes, while heating |
| Power-vent gas, plastic vent pipe and a blower on top | Blower motor before, during, and briefly after the burner runs | Yes, while running |
| Ultra Low NOx gas, plugs in, small motor on the flue | Damper motor opening or closing for a few seconds | Yes, brief |
| Standard electric tank | Element vibrating as water heats, especially with scale | Often; louder can mean scale |
| Standard gas tank without power | Burner roar while firing | Yes; a hum or buzz is unusual |
If the sound is popping, crackling, or rumbling rather than a hum, that is usually sediment on the tank bottom; see water heater sounds like rocks.
When a hum is a warning sign
- The motor hums but nothing turns. A blower or fan that hums without spinning may have a seized bearing or a failed capacitor. On a power-vent model, the heater should not fire and will usually show a code.
- Grinding, squealing, or rattling from a motor. Bearings are wearing. Book service before the motor stops.
- A loud buzz from the electrical area of an electric or hybrid heater, especially with a burning or hot-plastic smell. Turn off the breaker. Loose or overheated connections are a fire risk.
- The hum is constant even when no hot water has been used. A hybrid that runs all the time may have a dirty air filter or be in a space too cold for it. A power-vent blower that never stops is covered in water heater fan keeps running.
- The noise started with a code on the display or a change in the status light. Look the code up for your model first.
What you can check safely
On a hybrid model, clean the air filter on top of the unit with the breaker off, following your manual. A clogged filter makes the fan and compressor work harder and run longer, and A. O. Smith’s hybrid models show a filter code when it needs attention (see A. O. Smith hybrid problems). Make sure the unit sits level and is not touching a wall or shelf, which can carry vibration into the house. Normal heat pump sounds are covered in more detail in hybrid water heater noise.
On a power-vent model, check the outdoor vent termination for blockage. A partly blocked vent can change the blower’s sound and cause lockouts.
On an electric tank, note whether the sound happens only while the heater is recovering after hot water use. That pattern points to the elements and, often, scale on them in hard-water areas.
On any model, check whether pipes connected to the heater are vibrating against a joist or wall. Pipe straps and padding can quiet a hum carried through the plumbing.
What the technician will check
On a hybrid, the technician checks the fan and compressor mounts, the fan motor and its bearings, and whether the unit is running in the right mode for the space. On a power-vent heater, they inspect the blower motor, its mounting, and the vent for obstructions. On an electric tank, they check element connections for tightness and heat damage and may recommend flushing or replacing scaled elements. Element and wiring work is done with power isolated, because these heaters run on 240 volts.
Repair or replace
Blower motors, fan motors, damper motors, and elements are all replaceable parts. A failed compressor on a hybrid is a major repair; check the heat pump’s warranty before paying for it. A hum combined with a leak from the tank itself means the heater should be replaced.
Frequently Asked Questions
Q: Is it normal for my A. O. Smith hybrid to run for hours? A: Yes. Heat pump mode heats slowly but efficiently, so long run times after heavy use are normal, more so in a cool room. If it never stops, check the filter and the space around the unit.
Q: Why does my power-vent heater hum for a while after the burner shuts off? A: Power-vent blowers typically keep running briefly after the burner stops to clear the vent. If the blower runs continuously with no hot water being used, have it checked.
Q: Will flushing the tank stop the hum? A: Only if the sound comes from scale and sediment around the elements or on the tank bottom. Flushing does nothing for motor noise.
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: 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.
- A. O. Smith: standard electric no-hot-water diagnostic chart (opens in a new tab)Professional diagnostic context for standard electric storage heaters; not instructions to open or test your appliance.
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