Maintenance And Service; Pilot Orifice - Bosch WR 400-7.K Series Installation & Operation Manual

MAINTENANCE AND SERVICE

Approximately once a year, the Bosch should be checked,
cleaned and serviced as necessary. To remove the front cover,
first remove the incandescent particle tray, then pull off the
temperature adjustment knob and unscrew and remove the
plastic collar. THE FOLLOWING OPERATIONS SHOULD
BE PERFORMED BY A QUALIFIED SERVICE PERSON:
Vent System: Should be checked annually. Clean and repair
as needed.
Water Valve (Part #24): The water valve on this heater should
be serviced periodically. The frequency will depend on the
mineral content of the water and conditions of use or
whenever signs of corrosion appear at the gas and water
valve joint. Check that the water inlet filter (# 27 on figure
16, page 14) is clean. Diaphragm should be replaced every
7-8 years in residential applications and 3-5 years for
commercial applications. In acid water areas the venturi
should also be replaced at the same time.
Pilot Flame: The pilot flame should burn with a clean, sharp,
blue flame and should resemble the diagram in Fig. 12. If the
flame is soft and yellow the pilot screen may be dirty or the
pilot burner orifice may need to be cleaned or replaced. The
pilot flame should be approximately 2 inches long, extending
past the flame sensor. If the flame is too small, it will not
reach the flame sensor and the burners will note come on.
3mm
Pilot screen
Fig. 12 - Characteristic Pilot Flame
To clean the pilot burner and/or the pilot orifice: Turn off
the gas to the unit. Set the ON/OFF switch to OFF (position
). Remove the cover on the heater. To do so, pull of
the temperature adjustment knob and unscrew and remove
the plastic collar. Pull main cover out toward you and lift up
and out. The pilot orifice should be cleaned or replaced. Do
not enlarge orifice.
6 720 606 560
Do not use any wire or sharp object to clean orifices. Natural
gas orifices are large enough that you can usually clean them
by blowing through them. LP orifices, on the other hand, are
too small to clean and should be replacement. To access
the pilot orifice, remove 2 screws holding pilot assembly in
place. Then loosen compression fittings to expose pilot
orifice.
Main Burner Flames: The main burner flames should be
blue, with a more intense blue cone in the center core. Yellow
flames could be a sign of plugged or dirty burners, or a
blockage on the heat exchangers fins. If some burners have
yellow flames while others have good flames, it is likely that
dust, lint or spider webs have partially clogged the burner
Correct gap between
venturis. To clean the burners, contact a gas service person.
pilot burner tip and
electrode tip
Mineral Scale Build-up: In hard water areas the Bosch,
when operated at lower temperature settings, tend not to
Sparking plug
accumulate mineral buildup. If however, the heater is used
electrode
at the higher temperature settings and the water has a high
mineral content, periodic descaling may be necessary. The
heating coils should be flushed with a descaling solution.
Signs of scaling are rising outlet temperature and knocking
noises when water is flowing.
Flue gas safety device:
The flue gas safety device must not under any circumstances
be switched off, simulated or replaced by any other
component.
Operation and safety precautions
Flame sensor
The flue gas safety device checks the effectiveness of flue
gas extraction by the flue. If it is inadequate, the appliance
switches off automatically so that the combustion fumes do
Sparking
not escape into the room in which the appliance has been
plug
electrode installed. The flue gas safety device resets after a cooling-
down period.
If the appliance shuts down while in operation, ventilate the
room. Wait about 10 minutes then restart the appliance. If
the problem recurs, call an engineer. The user must never
make any modifications to the appliance.
Fig. 13 - Pilot burner with pilot orifice

PILOT ORIFICE

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