Bosch 125FX LP - Manual (Page 18)

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WATER IS TOO HOT
1. Temperature Selection too high
Turn the temperature adjustment knob counter-clockwise
(to the left) to lower the maximum water temperature.
Note: This will increase the activation flow rate.
2. Inlet water temperature is very warm (60°-75°F)
Reduce inlet gas supply to lower the heaters degree rise.
Note: Only the Model 125BS should be used if the inlet
water is preheated.
NOTE: Only the model 125B LPS or 125B NGS should be
used if the inlet water is preheated.
3. Inlet filter screen is clogged, restricting flow
Remove screen and clean it.
WATER IS NOT HOT ENOUGH
1. Temperature selection is set too low.
Change the setting. Turn the temperature selector knob
clockwise (to the right). Note: this will decrease the
activation flow rate.
2. Gas pressure is insufficient
It is extremely important for a tankless instantaneous
water heater to have the right size gas line to obtain the
correct gas pressure. 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 and see page
11 for proper gas line sizing.
3. Gas supply is insufficient
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. See gas pipe sizing chart
on page 11.
4. 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 “NO SPARK AT THE PILOT”
paragraph 4). Where automatic “anti-scald” valves are
required by code, lower the temperature setting on the
AquaStar as much as possible and balance the pressure
between cold and hot water after the AquaStar.
5. Parts in water valve are dirty or damaged, which will
prevent the gas valve from being fully opened.
If the internal water valve parts are damaged from water
quality or use, or there is evident corrosion where the water
valve and gas valve connect, then immediate service is
needed. See step 9 under the problem NO SPARK AT THE
PILOT. White vinegar should be applied first to any corrosion
before the loosening of screws.
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. Temperature balance valves
If the inlet water temperature to the water heater is very
warm the heater can produce temperatures that may be
found to be 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 manufactures 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 adjusted to produce
a more comfortable hot water temperature.
See SETTING THE WATER TEMPERATURE section.
3. Cold water is mixing with the hot water between the
AquaStar and the outlet
See #4 under “NO SPARK AT THE PILOT”.
4. Inlet water pressure is erratic due to inadequate supply
water pressure or saturated pressure tank on well
system
Check the inlet 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). Confirm that the pressure tank is not water logged.
5. Gas pressure is too low
See page 2 for correct specifications.
EXHAUST FAN DOES NOT OPERATE
1. Check the fuse (see fig 9)
2. Check all electrical connections
3. Check adjustment of microswitch (see Fig. 14)
FAN CIRCULATES WHEN HOT WATER IS SHUT
OFF
1. Check adjustment of microswitch (see Fig. 14)
FAN OPERATES WITHOUT WATER FLOW
1. Unplug the heater and first check that all electrical and
electronic connections in the heater are clean and tight.
2. Check adjustment of microswitch (see Fig. 14).
3. Control box may need to be replaced (see Fig 9). Check wire
connections and test operation of control box (see Fig 9).