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Measuring Gas Pressure; Water Connections - Bosch Model GWH 425 User Manual

Indoor model flow modulated with standing pilot suitable for heating potable water only -
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Measuring gas pressure

Connecting manometer
B Shut off gas.
B Remove front cover and locate inlet gas pressure
measuring point on the right side, see Fig. 15.
B Loosen screw from test point on the right side and
connect manometer tube on test point.
Fig. 15 Gas pressure measuring point
Inlet tap
Static pressure test
B Turn gas supply back on.
B Record static gas pressure reading on back page of
Operating pressure test
B Turn on all hot water taps served by the water heater.
B Run high hot water flow rate.
B Set flow control knob fully clockwise.
B Set slide control to the right.
B Record operating gas pressure reading on back
page of manual.
Gas pressures lower than 5.7" W.C. for Natural Gas or
10.5" W.C. for LP Gas will result in insufficient degree
rise to the hot water being used, and must be corrected.
See Gas Line Sizing under chapter 3.7.

Water connections

When facing the heater, the ½" cold water inlet is on the
bottom right and the hot water outlet is on the bottom
B Install unions or the Webstone service valves
when connecting plumbing to the water
heater. This will facilitate any necessary
cleaning and servicing.
6 720 608 034
Although water piping throughout your structure may be
other than copper, we recommend that copper piping
or suitably rated stainless steel flex line piping be used
for at least three feet before and after the heater (follow
local codes if more stringent). Never sweat any rigid
piping directly to or beneath the water connections,
damage can occur to the internal water valve from
heating of the pipe. Plastics or other PEX type plumbing
line materials are not recommended for connecting
directly to the water heater. Keep water inlet and outlet
pipes to no less than ½" (12.7mm) diameter to allow the
full flow capacity.
It is recommended that all water piping below the heater
be properly insulated to avoid heat loss.
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 heater.
Full port valves should be installed on both the cold
water supply and hot water outlet lines to facilitate
servicing the heater (see Fig. 16). For installation on a
private well system with the use of a pressure tank, the
lowest pressure range setting recommended is 30-50
psi (2.07 and 3.45bar).
Connecting the pressure relief valve (PRV)
The pressure relief valve supplied with the heater 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 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. 16. 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. 16 Plumbing connections and pressure relief
valve shown with optional Webstone service
Installation instructions



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