Tuesday, June 21, 2011

Bosch Aquastar 125B Water Valve Assembly

The Bosch Aquastar 125B gas tankless water heater was first manufactored back in the late 1980s. The 125B series has since been discontinued and replaced with newer compact models such as the 1600P gas tankless water heater, and later the Bosch Therm 520PN.

When the Bosch Aquastar 125B model first came out, it had a dual port brass water valve and then years later the Bosch Aquastar 125B series heater had a new single port polymer water valve which was much easier to service and maintain.

The replacement water valve for the 125B series heater that had a dual port brass water valve assembly is now a single port polymer watervalve retrofit kit. This water valve assembly retrofit kit is required for any heater with a serial number beginning with 380 or lower. This kit includes new cold and hot water pipes, washers and the single port polymer water valve so that it can be easily installed in the place of the old brass water valve. The new water valve retrofit kit for the 125B part number #8707002499 is available. Please visit the link.  There is also a service bulletin available for installation of the new retrofit water valve and the bulletin number is TWH-G1-37 and you can find this on the Bosch website at www.bosch-climate.us

The newer Bosch Aquastar model 125B gas tankless water heaters that had a serial number beginning with 381 or higher had the single port poly water valve. The new single port Polymer water valve for the 125B part number #8707002649 is available. Please visit the link.


  1. Regarding the serial numbers beginning with 380 or lower, does that include heading zeroes? For example would a S/N starting with 0900 be considered 900 (more than 380) or 090 (less than 380)?

  2. Dear Sir;
    Serial numbers beginning with numbers such as 090... 087... etc. were numbers before the 380. The older heaters had a metal Brass colored water valve and the newer 125B heaters after 380 had a new polymer water valve. I hope this helps and if you have any further questions please call us at 888-726-9752

  3. Hello I have a Bosch AQ-125 BLP...will this valve be compatible with Liquid propane?

  4. Thank you for your question. The answer on whether or not the Bosch part number 87070024990 is compatible depends on the serial number of your Bosch 125B tankless water heater.

    Please call us at 888-726-9752 to discuss.