Bosch parts are sold through licensed installers and Bosch dealers. Amazon and large plumbing distributors stock high-volume parts (flame rods, igniters, isolation valves, flow sensors) — these are DIY-replaceable. Internal parts (heat exchanger, gas valve, control board) are dealer-installed only.
The Bosch parts catalog
- Heat exchanger — primary failure mode after 12-18 years on scaled units. Dealer-installed
- Flame rod — the single most-replaced part. Behind 60% of Code A4 faults
- Igniter — direct spark ignition. Common Code A1 cause on older units
- Gas valve — modulating solenoid; dealer-only
- Control board (PCB) — model-specific, pre-flashed firmware
- Flow sensor — detects DHW flow to activate burner. Common Greentherm failure
Where to buy
- Amazon — flame rods, igniters, isolation valves, flow sensors
- Plumbing wholesaler — Ferguson, Hajoca, Winsupply
- Bosch dealer / authorized installer — full catalog
- Bosch America direct — warranty replacement only (parts ship to installer, not homeowner)
Bottom line
Flame rod, igniter, flow sensor are routine DIY replacements with the right part numbers. Heat exchanger, gas valve, PCB work goes through a Bosch-trained installer to keep warranty intact.