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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 “BURNERS DO NOT IGNITE
WHEN HOT WATER IS TURNED ON” 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 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

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. Make sure faucet aerators
or shower heads are free of minerals. 

Do not add any flow

restrictor to the shower head.

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

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.

4. Insufficient gas pressure

Check gas pressure requirements (page 2) and consult gas
service person.

PILOT LIGHT GOES OUT DURING OR IMMEDIATELY
AFTER HOT WATER HAS BEEN USED

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 12 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  repair
kit from BBTNA (part#8 703 406 204).

4. Water is too hot causing overheat sensor to shut

heater down

Reduce burners by sliding gas control to single flame
position or set control knob to a lower setting.

WATER IS TOO HOT

1

Burners are too strong

Note: If the inlet water is quite warm, slide gas valve control
to single flame symbol (    ) and the heater will function on
a minimum burner output.

2. Temperature selection is too hot

Turn the temperature adjustment knob to the left.

WATER IS NOT HOT ENOUGH

1. Temperature adjustment knob is set too low.

Change the setting. Turn the temperature adjustment knob
clockwise (to the right).

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 pages 2 and
10 respectively for correct gas pressure settings and where
gas pressures are taken.

Summary of Contents for AquaStar 38B LP

Page 1: ...sing property damage personal injury or death FOR YOUR SAFETY Do not store or use gasoline or other flammable combustible or corrosive vapors and liquids in the vicinity of this or any other appliance WHAT TO DO IF YOU SMELL GAS Do not try to light any appliance Do not touch any electrical switch do not use any phone in your building Immediately call your gas supplier from a neighbor s phone Follo...

Page 2: ...ition BOSCH is constantly improving our products therefore specifications are subject to change without prior notice AquaStar 38B LP and 38B NG Specifications Gas Input max 40 000 Btu hr min 20 000 Btu hr Water Connection 1 2 Thread fitting NPT H x W x D 25 3 8 x 10 5 8 x 9 1 8 Vent 4 Gas Connection 1 2 NPT thread Min Water Pressure 13 Psi at 1 3 GPM Max Water Pressure 150 Psi Shipping Weight 20 L...

Page 3: ...6 720 606 446 MINIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON COMBUSTIBLE MATERIALS FRONT VIEW SIDE VIEW AQUASTAR MODEL 38B MODEL 38B TOP A 12 FRONT B 4 BACK 0 SIDES 4 FLOOR C 12 VENT DIAMETER 4 ...

Page 4: ...or your safety and for proper heater operation you must provide an abundant supply of combustion air and a proper venting installation The heater may still operate even when improperly vented It will however be less efficient and could eventually damage the heater It could even result in human sickness or death due to oxygen deprivation and carbon monoxide poisoning Follow the guidelines below 1 P...

Page 5: ...tight construction all air should be taken from outside That would be 2000 cubic feet for the Aquastar 38B alone CLEARANCES The Aquastar 38 B is design certified for installation on a combustible wall and for installation in an alcove or closet with the minimum clearances to combustible and non combustible construction listed below A Top 12 inches 305 mm B Front 4 inches 102mm C Back 0 inches D Si...

Page 6: ...In unconfined spaces in buildings of conventional frame masonry or metal construction infiltration is normally adequate to provide air for combustion ventilation and dilution of flue gasses Identification labels are found on the shipping box and on the rating plate which is located on the right side panel of the cover Also each burner orifice is stamped with a number 79 for LPG and 120 for Natural...

Page 7: ... Horizontal sections must slope upwards at least inch for every foot of its horizontal length and be properly supported Keep the horizontal section short and avoid too many elbows The minimum vertical gas vent height allowed is 6 feet horizontal vent connectors and elbows are not to be considered in the total gas vent height All gas vent sections must be secured to each other with sheet metal scre...

Page 8: ...ollar must be used when penetrating a masonry chimney A Existing INTERIOR Masonry Chimney The metal gas vent pipe should be permanently mounted inside the masonry chimney Double wall Type B gas vent is recommended The masonry chimney may have to be tile or metal lined before the insertion of the gas vent pipe check local codes for clarification The lining material must be listed for use only with ...

Page 9: ...as to which it will be connected In the United States The installation must conform with local codes or in the absence of local codes the National Fuel Gas Code ANSI Z223 1 NFPA 54 In Canada The Installation should conform with CGA B149 INSTALLATION CODES and or local installation codes NOTE The Aquastar 38 B is supplied with a gas pressure regulator that must be installed on the heater before att...

Page 10: ...eak NOTE Do not apply soap solution to pilot filter screen or pilot orifice area If you have a leak shut off the gas After verifying that required gaskets are in place tighten appropriate fittings to stop leak Turn the gas on and check again with a soapy solution Never test for gas leaks using a match or flame MAXIMUM INLET GAS FLOW PRESSURE SETTING Above 4 500 ft consult your local gas supplier F...

Page 11: ...idual shut off valve OPERATINGINSTRUCTIONS Before proceeding with the operation of the heater make sure that the system is filled with water Open the cold water inlet supply to the heater fully Open a hot water faucet to permit the water to fill the heater and the piping and to eliminate the air trapped in the system Close the hot water faucet after the water flows freely and all the air has escap...

Page 12: ...emperature adjustment knob and unscrew and remove the knob collar Unscrew the central screw located at the bottom of the front cover Pull main cover out toward you and lift up and out Pull the air screen off wash it and blow any lint off See Fig 8 The pilot orifices should also be cleaned or replaced Do not enlarge the orifice Do not use any wire or sharp object to clean orifices Natural gas orifi...

Page 13: ...ved During this process press on the piezo ignition button separately until the pilot flame has ignited Main Burner Flames The main burner flames should be blue with a more intense blue cone in the center core Yellow flames could be a sign of wrong size gas orifices or dirty burners or a blockage on the heat exchangers fins If some burners have yellow flames while others have good flames it is lik...

Page 14: ...person to clean water valve or replace if corrosion is present PILOT LIGHTS BUT FLAME GOES OUT WHEN BUTTON IS RELEASED 1 Pilot push button was not pushed in far enough or was not held in long enough Slide the gas valve button to pilot position and depress this button Hold it pushed in for at least 15 seconds to give time for the pilot flame to properly heat the tip of the thermocouple 2 Pilot flam...

Page 15: ...s 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 bot...

Page 16: ...0 1 7 9 11 1 Heat exchanger 2 Pilot assembly 3 Burner manifold gas pressure test nipple 4 Pilot gas tubing 5 Main gas burner 6 Inlet gas pressure test nipple 7 Gas valve 8 Gas control slide 9 Piezo igniter 10 Temperature adjustment knob 11 Water valve 3 5 6 ...

Page 17: ...17 6 720 606 446 ...

Page 18: ...18 6 720 606 446 Fig 10 INTERIOR COMPONENTS DIAGRAM AND PARTS LIST ...

Page 19: ...051 11a Pilot air screen 8 700 507 055 12 Pilot orifice 8 708 200 005 NG 8 748 200 173 LPG 13 Pilot Tube 8 710 707 166 14 Thermocouple 8 747 202 083 15 Gas valve 8 707 011 456 LPG Gas valve 8 707 011 466 NG 16 Electromagnet 8 707 201 012 17 Thermocable 8 747 202 209 18 Water valve assembly 8 707 002 497 19 Pushrod 8 703 406 204 20 Water valve diaphragm 8 700 503 050 21 Slow ignition valve 8 708 50...

Page 20: ...20 6 720 606 446 Fig 11 Flow chart of Aquastar 38 B ...

Page 21: ...urnish a replacement part free of charge Shipping costs In addition to supplying the replacement part s BBTNA will provide ground service delivery for these parts Expedited or upgraded shipping will be charged to the customer Service labor costs This warranty does not cover any labor costs associated with service removal or re installation of part s All such costs must be borne by the Purchaser Ad...

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Page 24: ... E T A W D L I U B E R N E E R C S R E T L I F R E T A W T C E P S N I Y L B M E S S A T O L I P T C E P S N I Y L B M E S S A T N E V T C E P S N I R E N R U B N I A M T C E P S N I Replacement Parts available from BBT NORTH AMERICA Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Phone 800 642 3111 Fax 802 496 6924 www boschhotwater com techsupport boschhotwater com 2006 BB...

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