Troubleshooting - Bosch 940 ES Installation Manual

Troubleshooting

7 Troubleshooting
Warning: If you are unable to perform
the tasks listed below, or need
additional assistance please contact
your original installer or licensed gas
technician.
Inside the heater it is normal to find
i
unplugged wire connectors. These
connections are for adding accessories
such as cascading.
7.1 Introduction
Many of the questions customers ask regarding operation
of this unit can be answered by following the
troubleshooting steps as outlined below. Visit our web site
at www.bosch-climate.us
troubleshooting and service bulletins. For best results,
perform each step before proceeding to the next. The
suggested solutions may require that the cover be taken
off. (See Page 6 . Fig. 3 ).
7.2 Burner do not ignite when hot
water is turned ON
1. If the display is blank, verify power to outlet. (120VAC/
60Hz properly grounded circuit required). Verify that
the heater ON/OFF button is turned ON.
2. Verify the fuses in the control board are good. See
Section 4.2 , page 34 of the installation manual for fuse
locations.
3. Make sure cold water inlet connection is plumbed to
the right side of heater when facing unit. See Fig. 36 ,
page 29 .
4. A minimum of 0.5 gallons per minute (GPM) (1.9 l/m) is
required to activate the heater. A quart container
should fill in 25 seconds or less to activate heater. In
areas of warm inlet water temperatures, the heater may
increase activation rate to as high as 1.6 gallons per
minute (GPM) to prevent overshooting of set
temperature.
5. Clean inlet filter screen per chapter 6.2 , page 39 .
6. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house filters
are clear of debris.
7. The heater activates when the water flow through the
unit is at or above the required minimum of 0.5 GPM
(1.9 l/m). A crossover in the plumbing creates back
pressure on the water flowing through the heater.
Therefore, a higher flow rate than normal is needed to
force the heater to activate. To check for a plumbing
crossover, shut off the cold water supply to the water
heater. Then open all of the hot water taps served by
the heater. Wait 10 minutes and check for water flow
at taps. There should be no water flowing. Any
continuous flow of water, small or large, indicates a
44
for more detailed
crossover is present and must be corrected. Consult a
professional plumber for help in correcting a crossover.
Failing single lever faucets and mixing valves are
common causes of plumbing crossovers.
8. With the ON/OFF switch turned to OFF (O) position
and the power supply cord unplugged, remove the
unit's front cover (See Page 6 . Fig 3 ). Check wire
connections between the water valve, control unit and
electrode set. See chapter 12.2 , page 55 for location
of these parts.
9. Water heater in solar mode. If inlet water temperatures
exceed the water heater's set temperature, the burners
will not ignite and the solar mode indicator will show on
the display. See Fig. 53 , page 35 .
7.3 Water is too hot
1. Selected temperature on the unit is set too high. To
lower output temperature, see chapter 5.4 , page 36 .
2. Clean inlet filter screen per chapter 6.1 , page 38 .
3. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house filters
are clear of debris.
4. Confirm the heater's gas type coincides with the type
of gas being supplied. See Fig. 2 , page 6 for location
of rating plate.
5. Avoid restrictive outlets. Clean all showerheads and
faucet aerators. It may be necessary to upgrade to
higher flow rate shower heads if allowable by local
code.
6. In areas where the water has a high mineral content,
periodic descaling may necessary. See chapter 6.3 ,
page 39 for directions.
7. Ensure the outlet temperature sensor is making contact
and firmly mounted on the hot water pipe.
7.4 Water is not hot enough
1. Selected temperature on the unit is too low. To raise
output temperature, see chapter
2. Clean inlet filter screen. See chapter
3. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house filters
are clear of debris.
4. Confirm the heater's gas type coincides with the type of
gas being supplied. See Fig.
rating plate.
5. Check inlet gas particle screen for blockage at gas inlet
connection on bottom of unit.
6. Verify gas pressure is in accordance with specifications
in chapter 3.14 , page 33 . A gas pressure reading is
needed to proceed further. Contact your original
installer or a local certified gas technician to obtain this
reading.
7. Cold water is mixing into the hot water lines (plumbing
crossover). A plumbing crossover can unintentionally
5.4 , page 36 .
6.1 , page 38 .
2 , page 6 for location of
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