The heat exchanger is the centerpiece of every Takagi condensing unit and the part the 15-year T-H3/T-D2 warranty protects.
Failure modes
- Scale insulation (#1 cause): calcium scale blocks heat transfer. Burner runs hot; overheat (Code 121) trips
- Pinhole leak: after 12-15 years
- Freeze damage on outdoor units in power outages
Replacement cost
- Parts: $700-1,400 OEM
- Labor: $400-700
- Total: $1,100-2,100
Warranty
15-year T-H3/T-D2 heat exchanger / 10-year T-K/T-KJr / 1-year labor. Year-12 T-H3 failure: Takagi ships the part free; you pay $500 labor.
Catch: inspector evaluates for scale. Heavy scale = denied. Keep descaling documentation.
Bottom line
Protect the heat exchanger through maintenance. The 15-year T-H3/T-D2 warranty is industry-leading but defensible only with documented annual descaling.