Low Water Flow/Pressure; Hot Water Temperature Fluctuates At Tap; Noisy Burner/Heater During Operation - Bosch 940 ES Installation And Operating Instructions Manual

Troubleshooting
6. Verify gas pressure is in accordance with specifications in
chapter 4.14, page 45. 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 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.
8.5

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 or multiple sink 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 4.14, page 45. 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.
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 7.1, page 51.
5. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris.
58
8.6

Hot water temperature fluctuates at tap

1. Hot water is very hot out of the water heater, requiring
mixing in cold water in order to attain a usable hot water
temperature. The addition of too much cold will overpower
hot water flow from the tankless water heater.
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 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 inlet filter screen is clean and
clear of debris. See chapter 7.1, page 51 for inlet filter
cleaning 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 too much cold.
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 appliance when on
a well system.
8.7

Noisy burner/heater during operation

1. Sealed combustion leak. Make sure combustion cover is
securely fastened. Ensure the exhaust vent adaptor is
properly sealed with supplied gasket. Leaky seals create
improper combustion resulting in noise.
2. Improper venting. Venting that is unsealed, the wrong
material, too big in diameter or too long in run will result in
unstable burner flames and noise. Ensure venting is in
accordance with specifications in chapter 4.3, page 15.
940 ES – 6 720 644 930 (2019/09)