Most Likely Causes (Ranked)
AO Smith water heaters use brass or plastic drain valves. The plastic versions (common on Signature and ProLine models) are more failure-prone. Sediment from hard water gets trapped in the valve seat during flushing, preventing a full seal. Replacing with a brass ball valve ($10-15) is a permanent upgrade.
AO Smith ProLine models use glass-lined tanks that can develop bottom corrosion if the anode rod isn't maintained. The bottom of the tank is where sediment settles, creating hot spots that accelerate corrosion. Once the tank bottom rusts through, replacement is the only option.
All tank water heaters, including AO Smith, eventually corrode through the steel tank lining. The glass lining cracks from thermal stress, exposing bare steel to water. Sediment buildup insulates the tank bottom, creating hot spots that accelerate corrosion. Average tank life: 8-12 years; 6-8 with hard water.
The cold water inlet and hot water outlet connections on the AO Smith water heater can leak from loose fittings, failed dielectric unions, or deteriorated flex lines. Water runs down the tank body and pools at the base, mimicking a tank leak.
When cold water fills a hot AO Smith tank, the exterior sweats heavily. This is normal during heavy use or first recovery. It mimics a leak but is harmless.
How to Fix It
Tighten or Replace Drain Valve
$0-15 DIY / $100-200 Pro- 1Turn off power and cold water supply. Attach hose to drain valve.
- 2Try tightening the valve with a wrench. If plastic, consider replacing with a brass ball valve ($10-15).
- 3If replacing: drain the tank fully, unscrew old valve, apply Teflon tape to threads, install new valve.
- 4Refill completely before restoring power.
Replace T&P Relief Valve
$15-30 DIY / $150-250 Pro- 1Turn off power and water supply. Open T&P lever to drain pressure.
- 2Unscrew old valve with pipe wrench. Wrap new valve threads with Teflon tape.
- 3Install and reconnect discharge tube (must terminate 6 inches from floor, never capped).
Replace the AO Smith Water Heater
$800-2,500 DIY / $1,200-3,000 Pro- 1If the tank is corroded through, no repair is possible — replacement is required.
- 2Consider upgrading: heat pump water heaters use 60-70% less energy and qualify for up to $2,000 in IRA tax credits.
- 3A 50-gallon AO Smith replacement (same brand) is $600-1,200 for the unit. Installation adds $400-1,000.
When to Call a Professional
Never cap a T&P discharge tube — the valve prevents catastrophic tank explosion.
Always refill the tank completely before restoring power — a dry heating element destroys instantly.
Gas water heaters: if you smell gas, leave immediately and call your gas company.
Rusty water from hot taps means the AO Smith tank lining is failing — replacement is imminent.
How to Prevent It
Replace the anode rod every 3-5 years ($20-50 DIY) — the #1 way to extend any tank's life.
Flush 2-3 gallons from the drain valve every 6 months to remove sediment.
Set thermostat to 120°F to reduce sediment buildup and corrosion rate.
Install an expansion tank ($40-60) if your system has a check valve or PRV.
Frequently Asked Questions
AO Smith tank models typically last 8-12 years (6-8 with hard water). Their tankless models last 15-20 years. Anode rod replacement can extend tank life 3-5 years.
No. If the tank itself is leaking (corroded through), replacement is the only option. Valve and connection leaks can be repaired.
AO Smith offers 6-12 year tank warranties depending on the model line. Check your purchase date and model number on AO Smith's website. Keep your receipt.
Tank (AO Smith): $800-2,000 installed. Tankless: $2,000-4,500 installed. Heat pump: $1,500-3,500 installed. Tankless saves $80-150/year on energy.