Greentherm T9800SE 160/199 Cable Accessory for External Recirculation Pump

The Bosch Greentherm T9800SE 160 and the Greentherm T9800SE 199 gas tankless water heaters have an optional cable accessory that enables the heater to be connected to an external pump for recirculation application.  Direct recirculation through the tankless water heater is permissible, however, the heat exchanger warranty is reduced to 3 years.

This appliance has been designed to permit recirculation by controlling an external pump. For this function, the external pump must be electrically connected to the appliance - Bosch Greentherm External Pump Cable Accessory (7736504585).  The external pump will be sized by a contractor for the size of the application.

For further questions on the cable accessory or to place an order please call Global Protankless Supply at 866-289-4652.

Using Bosch Tankless for Domestic Hot Water Recirculation

Bosch tankless water heaters can be used in recirculation applications and there are many different set ups for this such as direct recirculation and indirect recirculation.  Certain models of the Bosch tankless water heaters are approved for direct recirculation and are listed below.  Please be aware that the heat exchanger warranty of 15 years will be reduced to 3 years for direct recirculation.  This is stated in the warranty section of the installation manual.   All of the Bosch tankless water heaters can be set up for an indirect recirculation application in conjunction with a mini tank, recirculation pump and aquastat as described in the image below. The warranty for recirculation through an indirect mini-tank and not directly through the heater is 15 years.

Bosch tankless water heaters approved for direct recirculation:
Bosch Therm C1210ES
Bosch Therm C1210ESC (Commercial Unit)
Bosch Greentherm C1050
Bosch Greentherm C950
Bosch Therm 940ES
Bosch Therm 830ES

Diagram for Recirculation Application:
(This schematic is for illustration only and must not be used for actual installation without appropriate engineering and technical advise from a properly licensed professional in the locality where the installation is made).

Bosch 345/450 ESR Tankless Recirculating Heaters

The gas tankless recirculating heaters, Bosch 345 ESR and the Bosch 450 ESR are temperature modulated and have electronic ignition.  The ESR stands for Electronic ignition, Sealed combustion and Recirculating.  These recirculating heaters are designed and approved for heating and recirculating potable water in conjunction with an indirect storage tank.

The 345/450 ESR are not approved or designed for closed loop heating applications.  The ESR units are not a tankless heater as they have no flow switch to respond to flow.  Instead it’s a recirculating water heater designed for tank loading applications.  When an AquaStat (not included) hooked up to a tank tells the ESR that water needs to be brought back up to temperature, the ESR will tell a circulator (not included) to turn on to create flow through the heater to reheat the water in the tank.   Please refer to the installation and applications manual. 

The Bosch 345 ESR recirculating heater is a 95K BTU unit and can deliver 3.5 GPM at a 45 degree rise.  Efficiency is 82%

The Bosch 450 ESR recirculating heater is a 120K BTU unit and can deliver 4.5 GPM at a 45 degree rise.  Efficiency is 81%

The temperature control range for both heaters can be set anywhere from 115°F (45°C) - 190°F (90°C)

The 345/450 ESR comes with a standard ¾” pressure relief valve. 

The 345/450 ESR has a special built-in freeze prevention cycle and is controlled by a sensor.  Freeze protection is always assured by the operation of the appliance.  If the primary NTC (temperature) sensor detects temperatures 9°F below the selected temperature, the appliance starts on minimum power until the sensor reads selected temperature.  In the case of minimum set point temperature then it will start at 41°F.  The use of non-potable additives like glycol is not approved.

The Bosch 345 ESR and the Bosch 450ESR must be installed indoors according to the provided installation manual.  The 345/450 ESR is NOT approved for outdoor installations. 

The Bosch 345/450 ESR recirculating heaters must be vented in accordance with the installation manual and require Category III 3” stainless steel sealed venting for the exhaust.  These heaters are direct vent units and must be vented directly to the outside in accordance with the installation manual.  These heaters cannot be combination vented with any other appliance.  The intake should be taken from the outside and 3”PVC or other material can be used only for the intake air.

The Bosch 345/450 ESR recirculating heaters are gas specific so they cannot be converted from one gas type to another.

Bosch Therm 660EF/660EFO Tankless Water Heaters

The new Bosch Therm 660 EF and Bosch 660 EFO are direct vent units.  These units take thier combustion air from the area they are installed in.  The 660EF/EFO are compact in design for space saving installations and are only 14" x 20 1/2" x 7".  The 660EF/EFO are designed and approved for reciculation and space heating applications.  The units have electronic ignition and come equipped with built in freeze protection.  The Bosch Therm 660EF vents either vertically or horizontally using 3" or 4" stainless steel venting #AL29-4C. 

The 660EF is manufactured in Japan and comes with a different vent connection than the 830ES, 940ES, etc.  The 660EF needs to be vented with single wall stainless steel venting and is designed to connect directly to "Bosch Vent".  However, a Z-Vent adapter (Part # 2SVSWB03) allows for the use of 3" Z-vent stainless venting to be used.  Global Pro Tankless Supply carries the adapter and all the Z-Vent stainless steel venting to install the Bosch Therm 660EF.  We are the exclusive distributor for the AQ5EF Side-wall Vent Kit for the Bosch 660EF tankless water heater.

The Bosch Therm 660EFO outdoor unit comes ready for installation and does not require any additional cap or venting.

Without the Z-Vent adapter (Part # 2SVSWB03), the customer would have to purchase different venting ("Bosch Vent") to use for the 660EF.

The Bosch Therm 660 EFO is our most compact outdoor model and is loaded with features you’d expect from Bosch, including freeze protection and built-in high temperature capability (160°F).

The Bosch Therm 660 EFO is a good replacement for the GWH425HNO and the 125BO as these units have been discontinued. 

The Bosch Therm 660EF and Bosch Therm 660EFO have an excellent warranty:

• 15 year limited warranty on heat exchanger; 3 year warranty if used in direct recirculating applications

• 15 year warranty on heat exchanger if used if recirculated through a storage tank such as the Ariston mini-tank

• 5 year warranty on all other parts