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Troubleshooting
21
• 4. 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 4.4 and 4.5 for
details in lowering temperature. If the problem
persists, go to www.boschhotwater.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.boschhotwater.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.boschhotwater.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.boschhotwater.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 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 installation manual. See
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.
