What You'll Need
- Flashlight
- Phone or camera to photograph the data plate
- Access to the water heater (move any stored items)
- Optional: manufacturer's website for serial number decoder
Step 1: Find the Data Plate
Every water heater has a data plate with the manufacturer name, model number, serial number, and capacity. On tank water heaters, this plate is usually on the upper portion of the tank, either on the front or side.
For tankless units, the data plate is typically on the front or bottom of the unit, sometimes behind an access panel.
Take a photo of the entire data plate. The serial number is what you need for determining age.
Step 2: Decode the Serial Number
Manufacturers encode the manufacture date in the serial number, but every brand uses a different format. Here are the most common brands and their codes.
A.O. Smith, State, and American Water Heaters
These brands use the first four digits of the serial number. The first two digits are the year, and the second two are the week.
Example: 1845A123456
- 18 = 2018
- 45 = Week 45 (early November)
This water heater was made in November 2018.
Rheem and Ruud
Rheem uses the first four digits in MMYY format (month then year).
Example: 0319B98765
- 03 = March
- 19 = 2019
This water heater was made in March 2019.
Bradford White
Bradford White uses a letter code for the year. The first letter indicates the year, and the second letter indicates the month.
Year codes (repeating 20-year cycle):
- A = 1984, 2004, 2024
- B = 1985, 2005, 2025
- C = 1986, 2006
- And so on through the alphabet
Month codes: A = January, B = February, C = March, etc.
Example: PG = 2019 (P) + July (G)
Whirlpool
Whirlpool typically uses the first four digits for year and week, similar to A.O. Smith.
Example: 1723A45678
- 17 = 2017
- 23 = Week 23 (early June)
When in Doubt
If you can't decode the serial number, search for "[manufacturer name] water heater serial number decoder" online. Most manufacturers have lookup tools on their websites. Building Intelligence Center and similar sites also have comprehensive decoder databases.
Step 3: Check for Warning Signs
Age matters, but condition matters more. An 8-year-old water heater in bad shape needs attention sooner than a well-maintained 12-year-old unit.
Visual Inspection
Look at the exterior of the tank and the connections. Check for:
- Rust or corrosion on the tank, especially around fittings
- Water stains on the floor beneath the unit
- Mineral deposits (white crusty buildup) on pipes and connections
- Burn marks or discoloration on gas units (indicates combustion problems)
Any active dripping or pooling water means the tank is leaking. This is not repairable. Start planning for replacement.
Water Quality Check
Run hot water from a faucet for 30 seconds, then fill a white bucket or bowl.
- Clear water: Good. No immediate concern.
- Rust-colored water: The tank is corroding inside. Failure is approaching.
- Sandy or gritty particles: Sediment buildup. The tank may be salvageable with flushing.
If only the hot water is discolored (not the cold), the problem is definitely the water heater.
Sound Check
Stand near the water heater while it's heating (you may need to run hot water first to trigger a heating cycle). Listen for:
- Rumbling or popping: Sediment on the tank bottom. Water trapped under sediment boils and creates noise.
- Whining or high-pitched sounds: Element problems (electric units)
- Banging: Water hammer (usually a plumbing issue, not the heater)
Rumbling sounds indicate significant sediment. Flushing may help if the tank isn't too far gone.
Performance Check
Think about how the water heater has been performing:
- Does hot water run out faster than it used to?
- Is the water not as hot as it should be?
- Are you running out of hot water with normal use?
Declining performance often means sediment is reducing tank capacity, heating elements are failing, or the unit is simply wearing out.
Step 4: Check the Anode Rod
The anode rod is a sacrificial metal rod that corrodes instead of your tank. When the rod is gone, the tank starts corroding. Checking this rod is the single best predictor of remaining tank life.
How to Check It
The anode rod screws into the top of the tank. You'll need a 1-1/16 inch socket and a long breaker bar to remove it. Turn off the water and release some pressure first.
If the rod is:
- Mostly intact with some pitting: Good condition. Check again in 2-3 years.
- More than 50% corroded: Needs replacement. Rods cost $20-50.
- Completely gone or just the wire core remains: Replace immediately. Tank damage may have already started.
Many homeowners have never checked or replaced the anode rod. If your water heater is 5+ years old and the rod has never been replaced, checking it should be a priority.
Step 5: Decide: Repair or Replace
Use this decision framework based on what you found.
Replace Now
- Active leak from the tank (not from valves or connections)
- Age 10+ years with any warning signs
- Rust-colored water from hot water only
- Age 12+ years regardless of condition (preventive replacement)
Water heater failures often cause water damage that costs far more than a new heater. When the signs point to replacement, don't wait for catastrophic failure.
Repair and Monitor
- Age under 8 years with minor issues (element replacement, thermostat, relief valve)
- Sediment buildup without rust-colored water (flush the tank)
- Anode rod depleted but tank shows no corrosion (replace the rod)
For repairs on units over 8 years old, weigh repair cost against the cost of replacement. If a repair costs more than 50% of a new unit, replacement usually makes more sense.
No Action Needed
- Age under 6 years with no warning signs
- Clear water, quiet operation, adequate hot water supply
- Anode rod in good condition
Continue annual maintenance: drain 2-3 gallons from the drain valve to remove sediment, and check the anode rod every 3 years.
Common Mistakes to Avoid
- Ignoring small leaks: Even slow drips from the tank itself mean failure is imminent. Valve and connection leaks can be repaired, but tank leaks cannot.
- Skipping the anode rod: This $30 part can extend water heater life by years. Ignoring it guarantees premature tank failure.
- Waiting until failure: Emergency replacements cost more and often mean cold showers while you wait for a plumber. Planned replacements let you shop for deals.
- Confusing brands: Many water heaters are made by the same company under different names. A.O. Smith makes State, American, and several other brands. They have the same serial number format.
What to Expect: Replacement Costs and Timeline
If replacement is needed, here's what to expect.
Tank Water Heater Replacement
A 40-50 gallon tank water heater replacement typically costs $800-1,500 installed. High-efficiency units, power-vented models, or difficult installations cost more. Budget $1,000-2,000 to be safe.
Installation takes 2-4 hours. Most plumbers can schedule within a few days for routine replacements, or same-day for emergencies (at higher cost).
Tankless Water Heater Upgrade
Switching from tank to tankless costs $2,000-4,500. The unit itself costs more, and installation often requires gas line upgrades, new venting, and electrical work.
Tankless units last longer (20+ years) and use less energy, but the upfront cost is significantly higher. The payback period depends on energy costs and hot water usage patterns.