Bosch 125B LPS - Manual (Page 16)

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See specifications on page 2. Unlike storage tank water
heaters, the burners of a tankless water heater must be very
powerful to heat water instantaneously since they do this
only at the time hot water is actually being used. It is therefore
imperative that the gas pressure requirement be met exactly.
Insufficient gas pressure will directly affect the water
temperature at the time of usage. See page 2 for correct
gas pressure settings.
3. Thermostat calibration is incorrect or thermostat is
defective.
Contact your service person or call CEC.
4. Btu input is too low due to insufficient gas supply
Make sure your main gas line is fully opened. If using LP
gas, be sure that the size of the propane tank is adequate to
supply the required gas pressure.
5. Cold water is mixing with the hot water between the
AquaStar and the outlet
Compare water temperature at outlet of the AquaStar (hold
the AquaStar’s outlet pipe with your hand) and at the tap. If
these two are very different, check for mixing valve or
plumbing crossover (see “MAIN BURNERS WILL NOT
IGNITE...” paragraph #6).
6. Parts in water valve are dirty or damaged, which will
prevent the gas valve from being fully opened.
Water valve maintenance needs to be performed, see #7
under BURNERS DO NOT IGNITE WHEN HOT WATER
IS TURNED ON.
HOT WATER TEMPERATURE FLUCTUATES / UNIT
DEACTIVATED
1. Unbalanced pressure in waterlines
The added restriction caused by the Aquastar 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, the lower hot water pressure may be overpowered
by a much higher cold water pressure, which may cause the
Aquastar burners to shut down (deactivate). Make sure faucet
aerators or shower heads are free of minerals.
Do not add any flow restrictor to the shower head.
Typically this deactivation symptom is a result of the hot
water being too hot to use comfortably. Warm inlet water
generally causes this. Lowering the control knob setting
and/or reducing the inlet gas supply to the heater should
correct this deactivation symptom.
2. Inlet water pressure is erratic due to inadequate supply
water pressure or saturated pressure tank on well
system
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). Confirm that
the pressure tank is not water logged.
3. Cold water is mixing with the hot water between the
AquaStar and the outlet
See #6 under “MAIN BURNERS DO NOT IGNITE WHEN
HOT WATER TURNED ON”.
4 . Insufficient gas pressure
Note required gas pressures (page 2) and consult gas service
person.