A.O. Smith Water Heater Drain Valve Replacement — What This Part Does
The drain valve sits at the bottom of your A.O. Smith water heater tank and lets you empty the unit for flushing sediment or performing service. You open it with a flathead screwdriver or by hand, attach a hose, and drain water to a bucket or floor drain. A.O. Smith uses plastic or nylon drain valves that handle hot, pressurized water daily.
These plastic valves crack, warp, or fail under constant heat and chlorinated water exposure. When the valve body breaks or the internal seal wears out, you get leaks at the tank base or the valve won’t close completely. Sediment buildup can also clog the valve or make it stick, and forcing a brittle valve open during service can snap the plastic body.
Signs It Needs Replacing
- Water dripping or pooling under the tank A steady drip or puddle at the base of the heater points to a leaking drain valve that no longer seals.
- Valve won’t close after draining After flushing the tank, water continues to seep or run from the valve even when you turn it fully clockwise.
- Cracked or visibly damaged valve body You see cracks, splits, or broken plastic around the valve housing or threaded connection.
- Valve turns freely but won’t open or close flow The handle or slot spins without resistance and water flow doesn’t change, meaning the internal mechanism has stripped or failed.
- Valve breaks when you try to open it Turning the valve with a screwdriver or wrench snaps the plastic body or handle off completely.
- Corroded or mineral-clogged threads Heavy mineral deposits or corrosion around the valve threads prevent proper sealing or make removal necessary for tank service.
How to Replace It
- Turn off electrical power to the water heater at the breaker.
- Close the cold-water supply valve feeding the tank.
- Attach a garden hose to the existing drain valve and run the hose to a floor drain, bucket, or outside.
- Open a hot-water faucet somewhere in the house to break the vacuum and allow the tank to drain.
- Open the tank drain valve by turning it counterclockwise with a flathead screwdriver or by hand.
- Let the tank drain completely, then close the hot-water faucet once drainage stops.
- Use an adjustable wrench or pipe wrench to unscrew the old drain valve counterclockwise from the tank threads.
- Thread the new drain valve clockwise into the tank opening by hand until snug, then tighten one additional quarter-turn with a wrench (do not overtighten plastic threads).
- Close the new valve fully, open the cold-water supply to refill the tank, and leave a hot faucet open until water runs steady to purge air.
- Check the new valve for leaks once the tank is full, then restore power to the heater.
The Part You Need
| Part | Notes |
|---|---|
| A.O. Smith drain valve (3/4-inch plastic or nylon) | Amazon | Check your water heater model and serial number on the data plate (usually on the front or side of the tank) and use it to look up the correct valve part number. Common replacements include A.O. Smith 9001870015, 100158121, and 100108605, but fitment varies by model. |
Related Error Codes
If this part is failing you may also see one of these codes:
- 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 you’re not comfortable draining 40 to 80 gallons of hot water or working with threaded tank fittings, call a plumber or water-heater technician. A pro can also inspect the tank for other corrosion or leaks while the unit is drained and verify that the new valve seats correctly without cross-threading or over-torquing the plastic threads. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.