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Bosch 125B LP Installation And Operating Instructions Manual page 13

Automatic instantaneous type water heaters for use with natural and liquefied petroleum gas
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7. Water valve parts may be dirty or components
Water valve and component parts must be totally free of
dirt. First check that the venturi is free of dirt particles. In
hard water areas, mineral deposits can eventually (3 to 5
years in hard water areas) corrode the water valve parts
to a point where they will need replacing. Any sign of
moisture or corrosion at the joint of the water valve and
the gas valve is a sign that the water valve assembly
components need to be replaced immediately. Note: Water
valve for model 125B is part# 8707002499 for both LP
and NG models. (Contact service person to clean water
valve or replace if corrosion is present).
1. Gas pressure too low
Very low gas pressure may be caused by low delivered
gas pressure, a jammed gas regulator or undersized gas
lines. If the gas lines are undersized, there may still be the
specified static gas line pressure. However when the water
valve opens, and gas enters the burners, the pressure could
drop sharply, causing the pilot flame to go out. Have a gas
technician confirm the gas pressure both static and at
maximum Btu output. Specifications for your heater are on
page 2.
2. Pilot may be dirty or weak
See Page 9 for instructions on pilot maintenance.
3. Burners are not shutting down immediately when
hot water is turned off
Note: If burners don't shut down immediately when the hot
water is turned off, the heater will overheat and the ECO
will shut-off the gas. Rebuild the water valve assembly.
Contact service person to clean or rebuild water valve.
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 too high (as with solar
preheated water)
Note: Only the AquaStar 125BS should be used if the inlet
water is preheated.
3. Reduce inlet gas supply when inlet water
temperature is very warm (60º-75ºF).
1. Temperature selection too low.
Change the setting. Turn the temperature adjustment 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 temperature rises on page 2.
3. Btu input is too low due to insufficient gas pressure
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 page 13 for locations
where gas pressures are taken.
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). 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. Parts in water valve are corroded so that the gas
passage is not fully opening.
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 and the outlet
See #6 under "Burners do Not Ignite When Hot Water Is
Turned On".
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 and 7 for correct specifications.

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