What should I do if I need to file a warranty claim for the ZWB 42-3?

Contact the heating contractor who installed your boiler and ask them to notify the distributor from whom they purchased it. If that's not possible, contact Bosch Thermotechnology Corp. at 50 Wentworth Avenue, Londonderry, NH 03053. You'll need a copy of your original invoice, proof of purchase, and documentation showing the original installation date and location. Defective components must be returned to BTC for inspection.