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Bosch 38B LP Installation And Operating Instructions Manual page 11

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1. Pilot push button was not pushed in far enough or
was not held in long enough
Slide the gas valve button ( ) to pilot position ( ) and
depress this button. Hold it pushed in for at least 15
seconds to give time for the pilot flame to properly heat
the tip of the thermocouple.
2. Pilot flame improperly aimed or is too weak so it is
not properly heating the tip of the thermocouple.
The Pilot flame should be a sharp blue flame and aimed
at the tip of the thermocouple so that it envelops 10 mm
(3/8 ") of the thermocouple tip. Pilot flame has to be properly
aimed at the thermocouple. See Fig 7.
3. Poor
Note: Electromagnet is part #8707201012 located on the
right side of the gas valve behind the piezo pushbutton
assembly. Check the tightness of the thermocouple
connection nut at the electromagnet: The Electro-magnet
connection is a large aluminum 17mm hex head nut. The
thermocouple end is a 5 mm brass nut which screws into
the 17 mm nut. Tighten the thermocouple nut snugly but
not too tight.
4. Poor circuit connections at the ECO. (Energy Cut-
Off overheat protection)
Oxidation or looseness of the ECO terminal connections
can result in millivolt current loss through the thermocouple
safety circuit. Clean terminals with very fine sand paper or
an eraser and reconnect ECO leads.
5. Faulty ECO (part #8707206040)
If cleaning the terminals attached to the ECO did not fix
the problem, connect a jumper wire between the two wires
and try to relight the pilot. If the pilot flame now remains
on, replace the ECO. If the flame still goes out when the
button is released, the ECO is not defective. Go to next
6. Faulty thermocouple (part #8747202083) or
electromagnet ) Unless these 2 parts are at least 8
to 10 years old, it is very unlikely that they are faulty.
Before testing, reconfirm that #2 is absolutely
correct, and that all connections are clean and tight.
To test the thermocouple, disconnect the thermocouple lead
to the ECO. Insert a multi-meter probe into the thermocouple
lead and attach or hold the other lead to the metal gas
valve (DC common). Light the pilot flame and hold button,
meter reading should be 24 mVDC or more. If the reading
is 24 mVDC or more the thermocouple is good. To test the
electromagnet, re-connect the thermocouple lead to the
ECO, light pilot and hold button while taking a reading
between the ECO leads and the metal gas valve (DC
common). The reading should drop to 19 mVDC or less. If
it does not, replace the electromagnet.
1. Pilot is not on.
Light the pilot. See lighting instructions.
2. Pilot lighting push button not turned to proper
Be sure that once the pilot flame is on, that the gas valve
button ( ) is slid all the way to the right to the ON position
3. Cold incoming water connection made to wrong
side of heater
Make sure cold water inlet connection is on the right side
of heater when you are facing heater.
4. Water flow rate at hot water tap is too low.
With the control knob set fully clockwise the Aquastar
model 38B requires ½ gallon per minute flow to activate
the burners. This is a flow which would fill a quart jar in
30 seconds.
5. Cold water inlet filter on heater is dirty.
Remove the filter and clean. This screen filter is located
at the inlet side of the brass water valve (fig. 10, #25).
Check and clean faucet aerators too.
6. Crossover in household plumbing
The AquaStar burner activates when there is sufficient
water pressure drop in the AquaStar water valve assembly
— ie. when a hot water faucet is opened. If there is a
crossover in the plumbing, the necessary pressure drop
in the AquaStar will be insufficient, or totally eliminated. A
plumbing crossover can be caused by a bad washer at a
single lever faucet or incorrect plumbing or a mixing valve
in the line, etc. which permits hot and cold water to mix in
the plumbing. The crossover will create a back pressure
in the system preventing the pressure drop in the Aquastar
(i.e. cold water is entering the water heater from both sides
and the burners will not come on). To confirm there is no
crossover in the plumbing, shut off the cold water supply
to the AquaStar. Open your hot water taps. There should
not be any water flowing. If there is water flowing, there is
a crossover in the plumbing. This is a plumbing problem,
not an Aquastar problem. Please contact your plumber.
7. Water valve parts may be dirty or components
Water valve and component parts must be totally free of
dirt. First check that the venturi is free of dirt particles. In
hard water areas, mineral deposits can eventually (3 to 5
years in hard water areas) corrode the water valve parts
to a point where they will need replacing. Any sign of
moisture or corrosion at the joint of the water valve and
the gas valve is a sign that the water valve assembly
components need to be replaced immediately. (Contact
service person to clean water valve or replace if corrosion
is present).



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