How Old Is Your Reliance Water Heater?
Reliance water heaters are made by A.O. Smith, so they use A.O. Smith's serial number format — the manufacture date is encoded in the first digits of the serial, and dating one takes seconds once you know the pattern. Enter your serial number in the free decoder above for an instant answer, or follow the guide below to read it yourself.
The same coding also applies to A.O. Smith's other brands, including State, American, and U.S. Craftmaster — all built in the same factories.
Where to Find the Serial Number
Check the rating plate (data plate) on the side of the tank — a silver or white sticker, usually in the upper half of gas and electric tank models. The serial number is printed next to the model number. On Reliance tankless and hybrid heat pump units, the plate is often on a side panel or behind the front cover.
Serials on older units can fade or get painted over. If yours is hard to read, take a photo and bump the contrast — you only need the first four digits to get the date.
How the Reliance Serial Format Works
The date code is year, then week, in the first four digits:
Worked example — 1811A002456:
18= 2018 (year)11= week 11 (mid-March)Aand the remaining digits = factory and production sequence- Result: manufactured in week 11 of 2018
Watch for letter prefixes. Some serials start with letters, or insert a letter inside the date block — these are factory or product-line codes, not part of the date. Skip leading letters and read the first four digits you find. For example, AB063014569 decodes to week 30 of 2006, and 1604J004619 decodes to week 4 of 2016.
Because the year is only two digits, a serial like 0414... could in theory mean 2004 or 2014. Compare the unit's condition and model number — and when in doubt, our decoder flags ambiguous cases instead of guessing.
Why Your Reliance Water Heater's Age Matters
- Lifespan. Tank water heaters average 8–12 years of service. Past that, internal corrosion makes tank failure — and a flooded floor — far more likely.
- Warranty. Reliance tank warranties typically run 6 to 12 years depending on the model, counted from the manufacture date. Decoding the serial tells you whether a repair might still be covered.
- Maintenance timing. Sediment flushing and anode rod replacement pay off most in the middle years of a tank's life; knowing the exact age helps you schedule them in time.
- Replacement planning. A unit past 10 years is on borrowed time. Knowing the date lets you shop for a replacement calmly instead of during an emergency.
Sources
Brand ownership confirmed by the A.O. Smith corporate brands page and the official Reliance Water Heaters site. Serial format details verified against the InterNACHI water heater dating chart and A.O. Smith's own production-date guidance.