Installation Manual

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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.
7.5 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 3.13 , page 32 . 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 6.1 , page 37 .
5. Inspect the water path for obstructions. Make sure all
showerheads, faucet aerators and whole house filters
are clear of debris.
7.6 Hot water temperature fluctuates
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
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 6.1 , page 37 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 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.
7.7 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
proper and in accordance with specifications in
chapter 3.3 , page 9 .
3. Lack of adequate combustion air. Drawing combustion
air from a room area of inadequate size will result in
unstable burner flames and noise. Improper use of
piping for 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 3.4 , page 23 , Combustion Air Requirements.
4. Cross contamination. Ensure that intake and exhaust
terminations maintain minimum required clearances
stated in the manual. Cross contamination between
intake and exhaust may cause unstable burner flames
and noise.
5. Lack of adequate gas pressure. Inadequate gas
pressure will cause the fuel-to-air mixture (CO
2
) to be
out of adjustment. This will result in unstable burner
flames and noise. Ensure gas pressure is in accordance
with specifications in section
3.13 , page 32 Measuring
Gas Pressure. A gas pressure reading is needed to