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Low Water Flow/Pressure; Hot Water Temperature Fluctuates At Tap; Noisy Burner/Heater During Operation - Bosch AQUA STAR 2400E LP Installation And Operating Instructions Manual

Temperature modulated with electronic ignition suitable for heating potable water only
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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 feed 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. Failing
single lever faucets and mixing valves are common
causes of plumbing crossovers.
8. Ensure that both temperature sensors are making
contact and firmly mounted on their respective cold
and hot water pipes. The hot water sensor should be
located on the horizontal section of the hot water
pipe before it exits the heater. The cold water sensor
is located on the first horizontal section of pipe as the
water comes into the heater.

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 3.8. 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 5.1.
5. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house
filters are clear of debris.
Hot water temperature fluctuates
at tap
Note: Temperature fluctuations from hot to cold during
use are typically caused by a restriction in the hot water
flow from the tankless heater. This slows the flow within
the tankless heater, decreasing it below the activation
flow rate, which shuts off the burners. The end result is
nothing but cold water coming out of the outlet. Follow
each step below before proceeding to the next. After
each step, test the hot water flow to see if it remains
constant without turning cold.
1. Check for restrictions in plumbing outlets, which
could limit hot water flow and may contribute to
heater deactivation. For sinks, remove faucet aerator.
Flush and clean screen and reinstall. For showers,
remove showerhead and flush. If plugged with min-
eral deposits, clean according to manufacturer's sug-
gestions or replace shower head. (If showerhead is
wand style/hand held, corrugated tube connecting to
head may be too restrictive. Use a larger tube or
replace with a normal showerhead.)
2. Clean inlet filter screen per chapter 5.2.
3. Check for a plumbing crossover by closing the
installer supplied cold water shut off valve (if none
installed, install before proceeding) and opening all
hot water taps supplied by the heater. Wait 5
minutes and check all taps. The water flow should
come to a complete stop at every tap. Any water
running, even a trickle, is a sign of a plumbing
crossover. Consult a local plumber or service person
for help. This condition must be corrected before the
heater can operate properly.
4. Confirm water pressure is adequate and constant..
Water pressure must stay above 30psi during heater
operation. For installation on a private well system
with the use of a pressure tank, the lowest pressure
range setting recommended is 30-50 psi (2.07-3.45
bar). The use of a pressure reducing/regulating valve
directly after the pressure tank is an effective way to
maintain constant water pressure to the water heater.
Watts brand 25AUB-¾" or N35B-¾" pressure
5. 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 such hot water tempera-
ture. In the event of any temperature instability at a fix-
ture using a temperature balancing valve, refer to the
valve manufacturer for instructions on internal adjust-
ment setting. An adjustment should be made to min-
imize 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.
Noisy burner/heater during
1. Sealed combustion leak. Make sure cover is securely
fastened. Ensure the exhaust vent adaptor is properly
sealed with supplied gasket. Leaky seals create
improper combustion resulting in noise.
6 720 608 263

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