Bosch 125FX LP Installation And Operating Instructions Manual page 16

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 (60º-75ºF)
Reduce inlet gas supply to lower the heaters degree rise.
Note: Only the Model 125BS 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. Water flow through the heater is higher than the
capacity of the AquaStar to heat it
Reduce the flow demand at the faucet. See flow rates at
specific temperatures on page 2.
3. 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 9 for proper gas line sizing.
4. 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 9.
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 "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.
6. Gas valve above the water valve is not fully
opening.
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.
16
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. Cold water is mixing with the hot water between
the AquaStar
See #4 under "NO SPARK AT THE PILOT".
3. Inlet water pressure is erratic due to inadequate
supply water pressure or saturated pressure tank on
well system
Check the inlet water pressure. On a private well, raise
minimum pressure setting to 30 psi. Confirm that the
pressure tank is not water logged.
4. Gas pressure is too low
See page 2 for correct specifications.
EXHAUST FAN DOES NOT OPERATE
1. Check the fuse (see fig 10)
2. Check all electrical connections
3. Check adjustment of fan microswitch
FAN CIRCULATES WHEN HOT WATER IS SHUT
OFF
1. Check adjustment of fan microswitch
and the outlet