Low Water Flow/Pressure - Bosch 940 ESO Installation Manual

Troubleshooting
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 faucets and mixing valves
are common causes of plumbing crossovers.
8. Ensure the outlet temperature sensor is making contact
and firmly mounted on the hot water pipe.

10.5 Low water flow/pressure

1. Too many hot water applications are being used
simultaneously or too much flow is demanded. The
water heater will effectively support two 2.0-2.5 GPM
shower heads simultaneously
applications. Greater draws will result in a water
pressure drop and reduced flow at taps.
2. Ensure that gas pressure is in accordance with
specifications in chapter
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.
3. If 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 inlet filter screen per chapter
5. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house filters
are clear of debris.
10.6 Hot water temperature fluctuates
or goes cold at tap
1. Hot water is very hot out of the tap, requiring mixing of
cold water in order to attain a useable hot water
temperature. The addition of too much cold water will
overpower the hot water flow from the tankless water
heater.
This slows the flow within the tankless water heater,
decreasing it below activation point, which shuts off the
burners. The end result is nothing but cold water
coming out of the outlet.
Consult www.boschpro.com 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 filter screen,
can result in unequal pressures between the cold and
38
or multiple
6.6 , page 24 . A gas pressure
9.1 , page 31 .
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 inlet
filter screen is clean and clear of debris. See
9.1 , page
chapter
instructions.
3. Heater deactivated by temperature balancing valves. If
the outlet water 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 heater can be lowered to
prevent the temperature balance valve from mixing in
sink
too much cold water.
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 40-60 psi (2.75 - 4.15
bar). Consult your installer or local plumber for effective
ways to maintain constant water pressure to the water
heater when on a well system.
10.7 Noisy burner/heater during
operation
1. Sealed combustion leak. Make sure combustion cover
is securely fastened. Ensure the outdoor cap is properly
sealed with supplied gasket. Leaky seals create
improper combustion resulting in noise.
2. Blocked venting. Ensure exhaust gases are properly
discharging to the outdoors via the louvered openings
on the outdoor cap and/or recess box.
3. Lack of adequate combustion air. Lack of combustion
air will result in unstable burner flames and noise.
Ensure adequate combustion air is provided to the unit
in accordance with specifications in Section
14 , Combustion Air Requirements.
4. Lack of adequate gas pressure. Inadequate gas
pressure will cause the fuel-to-air mixture (CO
out of adjustment. This will result in unstable burner
flames and noise. Ensure gas pressure is in accordance
with specifications in section
Gas Pressure. A gas pressure reading is needed to
proceed further. Contact your original installer or a local
certified gas technician to obtain this reading.
5. Verify proper CO
CO adjustments must be done by a certified gas
2
technician with a calibrated combustion gas analyzer.
31 for inlet filter cleaning
6.6 , page 24 Measuring
readings per chapter 9.4 , page 33 .
2
6 720 644 956
5.1 , page
) to be
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