Bosch 250 SXO NG - Manual (Page 20)

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20
Troubleshooting
Test by following 4th bullet under BURNERS DO
NOT IGNITE WHEN HOT WATER IS TURNED ON.
LOW WATER FLOW/PRESSURE
• Too many hot water applications are being
used simultaneously or too much flow is being
demanded
The 250 SXO will effectively support two 2.0-2.5
gpm shower heads simultaneously or multiple sink
applications. Greater draws will result in increased
pressure drop and reduced flow at taps. See flow/
temperature chart on page 17.
• Btu input is too low due to inadequate gas line
sizing
See specifications in chapter 2.8 - 2.9. The 250
SXO requires adequate gas pressure to reach
expected temperatures and flow rates, to
compensate for inadequate gas supply or lack of gas
pressure the 250 SXO will effectively reach the
selected output temperature, but only by reducing
the hot water flow rate. Its motorized water valve
makes this adjustment. Proper gas pressure will
need to be delivered before the motorized water
valve will allow greater flow rates through it. Lowering
the set temperature will also allow increased water
flow rate through the motorized water valve. See
flow/temperature chart on page 17.
• Cold water inlet filter screen is dirty
Remove water inlet filter screen and clean. The
screen is located at the inlet connection to the water
heater, disconnecting the main cold supply line at the
heater is required. Check and clean faucet aerator
screens too.
HOT WATER TEMPERATURE FLUCTUATES /
UNIT DEACTIVATED
• Unbalanced pressure in water lines
Any restriction caused by the water heater in the hot
water system can result in uneven pressures
between the cold and the hot. In such cases when
mixing cold water at the tap (manually or
automatically through a mix-type shower valve) the
lower hot water pressure may be overpowered by the
higher cold water pressure in the building and cause
the hot water flow rate to fall below the minimum rate
required. A pressure balance valve will help to
resolve this symptom.
• Temperature balance valves
If the outlet water temperature is set too high, the
heater can produce temperatures that are too hot. A
temperature balance shower valve can automatically
mix in cold water to reduce such hot water
temperature. In the event of any temperature
instability with the use of a temperature balance
shower valve, refer to shower valve manufacturer's
instructions for internal adjustment setting.
Adjustments should be made to the hottest setting in
the shower valve. Additionally the temperature
control of the heater can be lowered to produce a
more comfortable hot water temperature.
• 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 30-50 psi (2.07-3.45 bar). The use
of a pressure reducing valve after the pressure tank
is also an effective way to maintain a constant water
pressure to the water heater. Watts brand 25AUB-
¾” or N35B-¾” pressure relief valves or equivalent
are suggested.