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Troubleshooting
37
7Troubleshooting
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.boschpro.com for more detailed
troubleshooting. 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 does not ignite when hot
water is turned ON
It is recommended to use “Control board diagnostics”
page 36, chapter 6.7 as a tool for problem solving.
1. If the display is blank, verify power to outlet.
(120VAC/60Hz properly grounded circuit required).
Verify that the heater power button is pressed ON.
2. Verify the fuses in the control board are good. To
access fuses, the control board must be removed.
See chapter 4.2, page 27.
3. Make sure cold water inlet connection is plumbed to
the right side of heater when facing unit. See Fig. 14,
page 12.
4. A minimum of 0.65 gallons per minute (GPM) (2,5 l/
m) is required to activate the heater. A quart
container should fill in 23 seconds or less, from hot
water tap only, to activate heater.
5. Clean inlet filter screen per chapter 3.7, page 12.
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 0.65
GPM (2,5 l/m). A crossover in the hot and cold
plumbing pipes 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 each tap. There
should be no water flowing. Any continuous flow of
water, small or large, indicates a crossover is present
and must be corrected. Consult a professional
plumber for help in correcting a crossover. Failing
single lever faucet mixing valves are common causes
of plumbing crossovers.
8. With the power button pressed switch turned to OFF
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 51 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. 47,
page 28.
7.3 Water is too hot
1. Selected temperature on the unit is too high. To
lower output temperature, see chapter 5.4, page 29.
2. Clean inlet filter screen per chapter 6.1, page 31 to
increase flow through the heater.
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 5 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 32 for directions.
7. Ensure the 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 5.4, page 29.
2. Clean inlet filter screen. See chapter 6.1, page 31 to
increase flow through the heater.
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 5 for location
of 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 3.13, page 26. A gas
pressure reading is needed to proceed further.
Warning: If you are unable to perform
the tasks listed below, or need
additional assistance please contact
your original installer or a licensed gas
technician.
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