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Bosch 125B LP Installation And Operating Instructions Manual page 16

Automatic instantaneous type water heaters for use with natural and liquefied petroleum gas
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5. Crossover in household plumbing
The AquaStar burner activates when there is sufficient water
pressure drop in the AquaStar water valve assembly — i.e.
when a hot water faucet is opened. If there is a crossover in
the plumbing, the necessary pressure drop in the AquaStar
will be insufficient, or totally eliminated. A plumbing crossover
can be caused by a bad washer at a single lever faucet or
incorrect plumbing or a mixing valve in the line, etc. which
permits hot and cold water to mix in the plumbing. The
crossover will create a back pressure in the system preventing
the pressure drop in the Aquastar — i.e. cold water is entering
the water heater from both sides and the burners will not
come on. To confirm there is no crossover in the plumbing,
shut off the cold water supply to the AquaStar. Open your
hot water taps. There should not be any water flowing. If
there is water flowing, there is a crossover in the plumbing.
This is a plumbing problem, not an Aquastar problem. Please
contact your plumber.
6. 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 serviced immediately. Note: Water valve for model 125B
is part# 8707002649 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 14 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.
4. ECO (overheat sensor) tripped due to overheating
Re-ignite the appliance 10 minutes later. If it happens again,
contact your service person.
5. Flue gas safety device tripped
Ventilate the room and re-ignite the appliance 10 minutes
later. If it happens again, contact your service person.
1. Temperature Selection too high
Position the gas control slide to the single flame (
setting to reduce the burner output and/or turn the
temperature adjustment knob counterclockwise to lower the
maximum water temperature. Note: turning the knob
counterclockwise will increase the activation flow rate.
2. Inlet water temperature is very warm
Increased seasonal ground water temperatures will affect
the hot water output temperature. Reduce the burner output
if the inlet water is very warm (60-75F) by positioning the
gas control slide to the single flame (
temperature adjustment knob setting may also be lowered if
1. Temperature selection too low.
Change the setting. Turn the temperature adjustment knob
clockwise and/or slide the gas control to the winter mode
setting for increased burner output.
Note: This will decrease the activation flow rate.
2. 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 10 for locations where gas
pressures are taken.
3. 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.
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 "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.
5. 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
) setting. The
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