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4.12 Domestic Hot Water Recirculation - Bosch 940 ES Installation And Operating Instructions Manual

Indoor model natural gas/ liquefied petroleum (lp) gas
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recommends consulting a local water treatment professional
for water softening/conditioning options.
Max. Levels
TDS (Total
mg/l or ppm
Dissolved Solids)
Total hardness
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
Table 31
Connecting the pressure relief valve (PRV)
A listed pressure relief valve must be installed at the time of
installation. No valve is to be placed between the PRV and the
heater. No reducing coupling or other restriction may be
installed in the discharge line. The discharge line must be a
minimum of 4" above a drain and installed such that it allows
complete drainage of both the PRV and the line. The discharge
line must be placed where it will not cause any damage.
The location of the PRV must be readily accessible for servicing
or replacement, and be mounted as close to the water heater as
possible. See fig. 34. To install the PRV, a suitable fitting
connected to an extension on a "T" fitting can be sweated to the
hot water line.
Support all piping.
Fig. 34
Plumbing Connections (with shutoff valves) and
Pressure Relief Valve
940 ES – 6 720 644 930 (2019/09)
6.5 - 8.5
100 (6 grains)

4.12 Domestic hot water recirculation

Although recirculation directly through the tankless water
heater is allowed, temperature stability is improved by
recirculating through a mini-tank as shown in fig. 35. By using
the design in fig. 35, there is no recirculation of hot water
through the tankless water heater and therefore, does not
affect the heat exchanger warranty. Direct recirculation
through the tankless water heater is permissible, however, the
heat exchanger warranty is reduced; contact Bosch
Thermotechnology for further installation requirements. The
following drawing is provided to outline one possible
recirculation design using the water heater in conjunction with
a Bosch electric mini tank water heater. This schematic is for
illustration only and must not be used for actual Installation
without appropriate engineering and technical advice from a
properly licensed professional in the locality where the
installation is made.
Fig. 35
Recirculation application
[1] Full port isolation valve
[2] Circulator pump on timer
[3] Check valve
[4] PRV
[5] Expansion tank
[6] 940ES
[7] Bosch electric minitank
The use of a small electric mini-tank after heater (4-6 gallon
size) should be used for this application and designed so the
pump will circulate the water through the mini-tank and the
building's hot water return loop only. Timed or thermostatically
controlled operation of the pump is commonly done. Contact
Bosch Thermotechnology if further information is needed.
Installation instructions



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