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need for cold water mixed by turning the power
adjustment knob clockwise for lower hot water
temperatures. See chapter 4.4 and 4.5 for details in
lowering temperature. If the problem persists, go to
www.boschpro.com for a more detailed service bulletin
on this problem.
5. The overheat sensor (ECO) is tripped. The water
heater does not have a thermostat. If the inlet water is
preheated, the unit will overheat, stopping the flow of
gas. Plumb inlet with cold water only.
6. Flue gas sensor is tripped. Lack of adequate
combustion air or failure to vent properly by reducing
pipe diameter, improper use of elbows or exceed
maximum vent length will interrupt the flue gas sensor
circuit. Confirm venting and combustion air is in
accordance with requirements in this installation
manual.
7. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing the water to overheat and trip the
overheat sensor (ECO) shutting all gas flow. To descale
the heat exchanger, consult service bulletins on
www.boschpro.com.
8. The water valve assembly, which allows gas flow to
the burners, requires periodic maintenance (every 2-5
years depending on water quality and use). Visit
www.boschpro.com to purchase water valve rebuild kit
to service the water valve.
6.6
Hot water temperature fluctuates
at tap
1. Close installer supplied cold water shut off valve (if
none installed, install before proceeding). Open all hot
water taps supplied by the heater. Wait 5 minutes and
check all taps. Any water running is a sign of a plumbing
crossover. Consult local plumber or service person for
help correcting a plumbing crossover.
2. Check for a clogged inlet water filter screen. See
chapter 5.2.
3. Hot water is very hot out of the tap, requiring a lot of
cold water to be added with it in order to attain a
useable hot water temperature. The addition of too
much cold will overpower and slow the flow within the
tankless heater, decreasing it below activation point,
which shuts off the burners. The end result is nothing
but cold water coming out of the outlet. Reduce the
need for cold water mixed by turning the power
adjustment knob clockwise for lower hot water
temperatures. See chapter 4.5. If the problem persists,
go to www.boschpro.com for a more detailed service
bulletin on this problem.
4. The water heater is designed to modulate gas flow to
the burners when water flow varies. If the water
pressure in the home is erratic and the water flow is not
consistent while a tap is opened, then the temperature
of the hot water will fluctuate. The minimum water
6 720 608 036
pressure for the home should be 30psi or greater. For
installations on a private well system with the use of a
pressure tank, the lowest pressure range setting
recommended is 30-50psi (2.07-3.45 bar). The use of
a pressure reducing/regulating valve before the water
heater (directly after the pressure tank on well systems)
is an effective way to maintain constant water pressure
to the water heater. Watts brand 25AUB-3/4" or N35B-
3/4" pressure reducing/regulating valves or equivalent
are suggested.
5. If the inlet water temperature is not steady then the
hot water temperature from the water heater will
fluctuate. The water heater modulates its burners when
flow rate is changed. It does not have a thermostat and
will not adjust to changes in inlet water temperature.
6. If the inlet water temperature to the water heater is
above 70 F, the heater may produce outlet
temperatures that are too hot for most users. A
temperature balance shower valve can automatically
mix in cold water to reduce such hot water temperature.
This can slow the flow within the tankless water heater,
decreasing it below activation point, which shuts off the
burners. In the event of any temperature instability with
the use of a temperature balance shower valve, refer to
shower valve manufacturer instructions for internal
adjustment setting. An adjustment should be made to
minimize the amount of cold water the valve is adding.
7. The gas pressure also needs to be stable and
adequate. Ensure gas pressure is in accordance with
specifications
in
the
chapter 3.9. A gas pressure reading is needed to
proceed further. Contact your original installer or a local
certified gas technician to obtain this reading.
6.7
Water is too hot
1. Verify gas type indicated in the rating sticker located
on the cover's right hand side, coincides with the gas
type you are using. NG is a natural gas unit and LP is
for liquid propane (See chapter 2.2).
2. Adjust the power adjustment knob clockwise for
cooler temperatures. If the water is still too hot, the
temperature adjustment knob maybe set too high.
Lower the setting and test the water temperature. This
dial turns counterclockwise for lower temperatures and
clockwise for higher temperatures.
3. Inlet water is preheated. This model does not have a
thermostat and will not modulate flame height in order
to prevent overheating. It is designed for a cold water
feed only. Replumb the heater with cold water to the
inlet.
4. Increase flow rate. Restrictions in the water path can
slow the flow of water through the heater, resulting in
very hot outlet temperatures. Restrictive showerheads
and faucet aerators should be cleaned out or upgraded
with less restrictive ones. In addition, the inlet filter on
the water heater should be cleaned and inspected. See
chapter 5.2.
Troubleshooting
installation
manual.
See
21
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