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32 | Troubleshooting
5. Avoid restrictive outlets. Clean all shower heads 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 9.3, page
30 for directions.
10.4 Water is not hot enough
1. Selected temperature on the unit may be too low. To raise
the output temperature, see chapter 8.4, page 28.
2. Clean inlet filter screen. See chapter 9.1, page 29 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 9 for the location of the
rating plate.
5. Check the inlet gas particle screen for blockage at inlet of
the gas connection on bottom of unit.
6. Verify the gas pressure is in accordance with specifications
in chapter 6.6, page 25. 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 may be mixing into the hot water lines
(plumbing crossover). A plumbing crossover can
unintentionally mix cold water with the hot water leaving
the heater. The end result is a cooler water temperature
than desired. 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 all taps for water flow. There should be no water
flowing. Any continuous flow of water, small or large,
indicates a crossover 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.
10.5 Low water flow/pressure
1. Hot water demand may be in excess of the water heater
capacity. Refer to specification table in chapter 3.2 for hot
water flow rates for your water heater. Higher flows result
in higher pressure drop.
2. Ensure that gas pressure is in accordance with
specifications in chapter 6.6, page 25. A gas pressure
reading is needed to proceed further. Contact your original
installer or a local certified gas technician to obtain this
reading. If gas pressure is inadequate, the water heater will
close its motorized water valve, reducing the hot water flow
rate in an attempt to reach the selected output
temperature.
6 720 817 281 (2017/05)
3. If the selected temperature on the unit is set too high for the
demanded flow rate, the water heater will close its
motorized water valve, reducing the hot water flow rate in
an attempt to reach the selected output temperature.
Lowering the selected temperature will allow the motorized
water valve to open up for increased water flow rate.
4. Clean the inlet water filter screen per chapter 9.1, page 29.
5. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris.
10.6 Hot water temperature fluctuates at tap
1. If the water heater set point temperature is high, mixing at
the faucet could deactivate the water heater. The addition
of too much cold will overpower hot water flow from the
tankless water heater reducing its flow below the activation
point.
If this slows the flow through the tankless water heater
below its activation point, it will shut off the burners. The
end result is nothing but cold water coming out of the
outlet. Consult www.bosch-climate.us for a detailed
service bulletin on overcoming temperature fluctuations.
2. Unbalanced pressure in water lines. Any restriction in the
water heater, such as a clogged inlet water filter screen,
can result in unequal pressures between the cold and hot
water lines. In such cases, when mixing in the higher
pressure cold water at the tap, the lower pressure hot
water can be overpowered. This will shut down the burners
because the hot water flow rate fell below the minimum
flow rate required for activation. Verify that the inlet water
filter screen is clean and clear of debris. See chapter 9.1,
page 29 for inlet water filter cleaning instructions.
3. The water heater may be deactivated by temperature
balancing valves. If the water heater's set point
temperature is set too high, the heater can produce
temperatures that are too hot. A temperature balance
shower valve will automatically mix in cold water to reduce
the hot water temperature. In the event of any temperature
instability at a fixture using a temperature balancing valve,
refer to the valve manufacturer for instructions on internal
adjustment setting. An adjustment should be made to
minimize the amount of cold water the valve is adding.
Additionally, the temperature setting on the water heater
can be lowered to reduce the amount of cold water that the
temperature balance valve mixes in.
4. Inlet water pressure is erratic due to fluctuating supply
water pressure. For installation on a private well system
with the use of a pressure tank, the lowest pressure range
setting recommended is 30 - 45 psi (2.06 - 3.1 bar).
Consult your installer or local plumber for effective ways to
maintain constant water pressure to the appliance when on
a well system.
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