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Water Quality; Domestic Hot Water Recirculation - Bosch 940 ESO Manual

940 eso - natural gas / 940 eso - liquefied petroleum (lp) gas
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20 | Installation instructions
Fig. 25
Hot connection
Cold connection
Fig. 26 Water filter
Water filter
▶ The use of unions when connecting both water pipes to the inlet and
outlet connections is required. This will facilitate any necessary
▶ Plastic or PEX type plumbing line materials are not suitable for
connecting directly to the water heater.
▶ Although water piping throughout the building may be other than
copper, we recommend that copper or suitably rated stainless steel
flex line piping be used for the water connections for 1.5' on either
side of the water heater (follow local codes if more stringent).
▶ Never sweat any piping directly to or beneath the water connections,
as damage will occur to the internal water valve from heating of the
▶ Keep water inlet and outlet pipes to no less than ¾" (19.05mm)
diameter to allow the full flow capacity.
▶ If the cold and hot connections to the heater are reversed, the heater
will not function. Be certain there are no loose particles or dirt in the
piping. Blow out or flush the lines before connecting to the water
▶ Full port shutoff valves should be installed on both the cold water
supply and hot water outlet lines to facilitate servicing the heater (see
fig. 27).
▶ For installation on a private well system with the use of a pressure
tank, the lowest pressure range setting recommended is 40-60 psi
(2.75 - 4.15bar).
6 720 644 956 (2016/05)

Water quality

Water quality can have an impact on appliance longevity and may void
the manufacturer's warranty.
For water analysis data call your local water department, or if on a well,
have well water analyzed periodically. If water quality exceeds one or
more of the values specified below, Bosch recommends consulting a
local water treatment professional for water softening/conditioning
TDS (total Dissolved Solids)
Total hardness
Table 11
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. 27. 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. 27 Plumbing Connections (with shutoff valves) and Pressure Relief

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. 28. By using the design in fig. 28, 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
Max. Levels
6.5 - 8.5
mg/l or ppm
mg/l or ppm
100 (6 grains)
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
mg/l or ppm
940 ESO



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