Find Your Bosch Tankless Water Heater's Age
Bosch has sold tankless water heaters in North America for decades under names like AquaStar, Therm, Greentherm, and Tronic — and it has used two completely different serial date codes along the way. Enter your serial number in the free decoder above for an instant answer, or follow the guide below to read it yourself.
Where to Find the Serial Number
Look for the rating data plate on the front or side of the unit, sometimes behind a removable cover. The serial number sits next to the model number, gas type, and BTU rating. One useful shortcut: on units made from 2010 onward, Bosch prints the manufacture date in plain text on the data plate, so if you see "Mfg Date" or similar, you're done — no decoding needed.
How the Bosch Serial Format Works
Pre-2010 units put a three-digit date code at the very start of the serial (or right after a leading FD). All three digits matter: the first digit is the year digit, and the last two encode the month on a base that shifts with the decade — which is how Bosch keeps 1998 distinct from 2008:
| Code range | Years | Month |
|---|---|---|
| 861–872 | 1998 | last two digits − 60 |
| 961–972 | 1999 | last two digits − 60 |
| 081–092 … 781–792 | 2000–2007 | last two digits − 80 |
| 881–892 | 2008 | last two digits − 80 |
| 981–992 | 2009 | last two digits − 80 |
Worked example — 388123456:
- First three digits =
388 - Leading
3+ month code88→ 88 − 80 = August, year 2003 - Result: manufactured in August 2003
Worked example — FD687400341:
- Ignore the leading
FD; the date code is687 - Leading
6+ month code87→ 87 − 80 = July, year 2006 - Result: manufactured in July 2006
2010-and-newer units use a longer, multi-segment serial where the date code is always the 5th through 7th digits, regardless of where the dashes fall or whether they're there at all.
Worked example — 8370-853-000213-7736502725:
- Digits 5–7 =
853 - Per Bosch's current chart, 853 = May 2018
- Result: manufactured in May 2018
The modern chart runs through the 2020s with the same no-collision trick (for example, 011 = November 2010, 455 = July 2014, 174 = June 2021), and our decoder applies it automatically. If your serial doesn't match either published format — very old pre-1998 units, for instance — the decoder will tell you honestly rather than guess, and Bosch technical support can date the unit from the full serial number.
Why the Age of Your Tankless Water Heater Matters
- Lifespan. Bosch tankless units typically last 15–20 years — far longer than tank-style heaters — but only with upkeep. A late-1990s AquaStar is well past its design life; a 2015 Greentherm is mid-career. The serial settles which you have.
- Warranty. Bosch heat-exchanger warranties commonly run 10–15 years depending on the model and registration. Decoding the serial tells you whether a repair might still be covered before you pay for a service call.
- Maintenance timing. Descaling the heat exchanger matters more every year in hard-water areas. An accurate manufacture date helps you judge whether a flush, a repair, or a replacement is the sensible spend.
- Buying a home. A tankless unit past 15 years is a near-term replacement cost worth knowing about before closing — and the serial number is the fastest way to prove it.
Sources
Serial format details verified against the Building Intelligence Center's Bosch water heater dating guide (pre-2010 three-digit chart, FD-style serials, and the note that 2010-and-newer data plates print the date outright) and the Building Intelligence Center's Bosch HVAC dating guide (the 2010-and-newer chart Bosch points tankless owners to, where the date code is always the 5th–7th digits of the serial; parent company Bosch Thermotechnology Corp., sister brand Buderus).