A.O. Smith Water Heater Popping Noise — What’s Happening
A popping or rumbling noise from an A.O. Smith water heater is a symptom, not a fault code. It typically means sediment has built up at the bottom of the tank and is interfering with water and steam flow. As the tank heats, steam bubbles form under the sediment layer and then pop as they escape, creating the noise you hear.
A.O. Smith notes that for some gas units, the noise can also come from the vent or blower area, or from loose components in the combustion path. If the popping is accompanied by hissing or sizzling sounds, that can point to a leak rather than sediment buildup.
Most Likely Causes
- Sediment buildup in the tank The primary cause is sediment at the bottom of the tank trapping steam bubbles that pop as they release during heating.
- Hard water and high mineral content Hard water accelerates sediment accumulation, which is why regular flushing is necessary to prevent noise and maintain efficiency.
- Venting issues on gas units On gas models, noise can come from debris or blockages in the vent or blower wheel area rather than the tank itself.
- Loose mechanical parts or joints Loose screws, joints, or components in the burner assembly or combustion path can create popping or rattling sounds during operation.
- Debris in the burner area Dust, rust, or other debris in the gas burner can cause unusual combustion sounds that resemble popping.
- Leak at element or valve connection A hissing or sizzling noise that sounds like popping may actually be water leaking onto a heating element or hot surface.
How to Diagnose and Fix
- Verify whether the unit is electric or gas, then listen for when the noise occurs during the heating cycle or at startup.
- Inspect the base, heating element areas, burner assembly, and all connected piping for visible leaks or wet spots.
- If there is no leak and the noise is a pop or rumble, shut off power or set the gas control to Pilot and close the cold water supply.
- Let the unit cool if needed, then attach a hose to the drain valve and route it to a safe drain location.
- Open a hot water faucet somewhere in the house to prevent vacuum lock, then open the drain valve and drain the tank completely.
- Reopen the cold water supply to flush remaining sediment until the water runs clear, then close the drain valve and refill the tank.
- Restore power or gas operation and listen for the noise again during the next heating cycle.
- If the noise persists on a gas unit, check and clean the vent and blower wheel, confirm they move freely, and inspect the burner assembly for debris or loose components.
Parts You Might Need
| Part | Notes |
|---|---|
| Aluminum-zinc anode rod | Amazon | A.O. Smith suggests this as an alternative if you see bead-like material during draining or have corrosion issues. |
| Drain valve | Amazon | Used during flushing. Replace if it leaks or does not seal properly after the flush procedure. |
| Vent or blower wheel components | Amazon | For gas units where the noise comes from the combustion or vent path rather than sediment in the tank. |
Related Error Codes
If your appliance also shows a code on the display, these match this problem:
- A O Smith Water Heater E2 error code
- A O Smith Water Heater E4 error code
- A O Smith Water Heater E6 error code
When to Call a Pro
If the popping noise continues after a thorough tank flush, or if you hear hissing or sizzling that points to a leak, call a qualified technician. For gas units, any work involving the burner assembly, vent system, or blower wheel should be handled by a professional to avoid combustion safety issues. If you are uncomfortable draining the tank yourself or the unit has not been flushed in several years and the sediment is heavy, a tech can perform the flush and inspect the anode rod and other internal components at the same time. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.