GBT A2-035 Manual

Note: Place a copy of these instructions adjacent to the boiler/heater; notify the owner to keep for future reference.
If Shipping Damage is noted, receiver must make damage claim on Bill of Lading (see page 6).
918 West Walnut St. Danville, Kentucky 40422
Visit Us On The Web: www.gbt-inc.com
For Customer Service Please Call: 859-236-3181
W3260001 Rev. D Effective May, 2011
INSTALLATION & OPERATING
INSTRUCTIONS
For All A2000 Series Water
Heaters & Water Boilers
WARNING:
If these instructions are not followed exactly, a fire or explosion may result causing
property damage, personal injury or death.
FOR YOUR SAFETY: Do not store or use gasoline or other flammable vapors and liquids or
other combustible materials in the vicinity of this or any other appliance. To do so may result in
an explosion or fire.
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. Follow the gas supplier’s
instructions.
•If you cannot reach your gas supplier, call the fire department.
Installation and service must be performed by a qualified installer, service agency or the
gas supplier.

Page 1
Safety messages and instructions located in this manual and on the heater/boiler provide warnings to
you and others of potential hazards. Before installing, operating or servicing this heater/boiler, it is
important to read and understand these safety instructions and messages.
The safety alert symbol alerts you to potential hazards. The message that follows this
symbol must be obeyed to avoid possible injury or death.
DANGER indicates the presence of immediate hazards which, if not avoided, could result in
severe personal injury, death, or substantial property damage.
WARNING indicates a potentially hazardous situation which, if not avoided, could result in
severe personal injury, death or substantial property damage.
CAUTION indicates a potentially hazardous situation which, if not avoided, may result in
minor or moderate injury, or property damage.
Qualified Installer: Must have the ability of a licensed tradesman in the fields of gas supply, plumbing and
venting, including a thorough understanding of the National Fuel Gas Code as it relates to gas fired water
heaters and boilers. The installer must thoroughly review and understand this manual.
Service Agency: Must have the ability of a licensed tradesman in the fields of gas supply, plumbing and
venting, including a thorough understanding of the National Fuel Gas Code as it relates to gas fired water
heaters and boilers. The servicer must thoroughly review and understand this manual and perform service and
repairs strictly in accordance with the manufacturer’s service instructions.
Gas Supplier: A natural gas or propane Utility or service company that supplies gas for water heater and boiler
appliances, typically having responsibility for the inspection and code approval of the gas piping up and
including the meter or Propane storage tank. Many gas suppliers meet the requirements of a Qualified Installer
or Service Agency.
Verify that the gas hooked up to the appliance is the same type specified on the Name Plate
label, located on the heater/boiler.
Should overheating occur, or the gas valve fails to shut, do not turn off the electrical supply to
the heater/boiler. Shut off the gas supply at a location away from the heater/boiler.
Do not use this heater if any part has been under water. Have the heater/boiler inspected by
a qualified service technician. Replace any electrical or gas control system which has been
under water.
This unit requires an inlet water temperature of at least 120
o
F (49
o
C) to avoid flue gas
condensation. Condensation may cause pre-mature heat exchanger failure. Prolonged
operation of this heater/boiler with return temperatures below 120
o
F will void the warranty.
Maintain the area surrounding the heater/boiler clean and free of combustible materials,
gasoline, and other flammable liquids or vapors. The heater/boiler should never be covered.
This heater/boiler requires a constant supply of fresh air for proper combustion. Failure to
provide an adequate flow of fresh air may result in series injury or death.
SAFETY

Page 2
INTRODUCTION …………………………………………………………………………… 4
General
Dimensions & Specifications
Model Identification
Ratings & Certifications
INSTALLATION ……………………………………………………………………………. 6
Product Receipt
High Elevation
Location & Placement
Combustion Air Requirements
Electrical Requirements
Gas Requirements
Water Connections
Venting System
START-UP & OPERATION ……………………………………………………………... 15
Pre-Start Checklist
Filling The System With Water
Purging Air From Gas Lines
Preparation
Start-Up
Shut-Down Procedure
Operation
MAINTENANCE & INSPECTION …………………………………………………….. 22
Heat Exchanger
Burner & Pilot Flame
Gas Manifold Pressure
Vent System
Burner & Flue Passageway
Pressure Relief Valve
High Temperature Switch
Flow Switch
Heat Exchanger Protections
Condensation
Removal of Existing Appliance
TROUBLESHOOTING …………………………………………………………………. 25
DIAGRAMS ………………………………………………………………………………. 29
Typical Hydronic Heating Loop Piping Diagram
Low Temperature Heating Loop Piping Diagram
Single Heater Domestic System Piping Diagram
Dual Heater Domestic System Piping Diagram
By-Pass Loop Plumbing For Low Temperature Systems
Wiring Diagrams
PARTS LIST ………………………………………………………………………….…. 37
WARRANTY INFORMATION …………………………………………………………. 41
TABLE OF CONTENTS

Page 3
Thank you for purchasing an A2000 Series water heater/boiler from Green Boiler Technologies. Your model
was proudly built in the United States with high quality components and craftsmanship. With the proper
installation and maintenance, your A2000 heater/boiler will provide years of outstanding performance.
The A2000 series water heaters and water boilers utilize efficient copper fin-tube heat exchangers and are
certified as Category I Appliances. Category I equipment utilizes natural draft to remove flue gases without need
of a fan or draft inducer, and has flue gas temperatures more than 140°F above the dew point.
The unique design of the appliance provides excellent heat transfer and a small footprint. The heat exchanger
resists build-up of lime scale and allows de-liming without disassembly of the unit.
DIMENSIONS & SPECIFICATIONS
Model A B C D E F G H K
A2-035 7 17 ½ 34 ½ 38 58 9 24 10 29
A2-050 8 16 ½
33 42 69 10 28 18 ½ 33
A2-070 10 ¼
13 ¼ 33 38 ¾ 66 12 32 25 36 ¼
A2-097 6 ¾ 17 ¾ 38 41 ¼ 77 ¼ 16 35 20 43
A2-120 7 17 ½ 44 ½ 48 ½ 84 ½ 16 35 22 43
A2-140 7 17 ½ 44 ½ 48 ½ 100 ½ 18 35 22 43
Dimensions in Inches; Dimensions For Units With Standard Gas Train
Model BTU
Input **
GPH @
100
o
Rise
Gas
Connection
Water
Connection
Vent
Diameter
Shipping
Weight *
A2-035 350,000 336 1 1 ½
9 460
A2-050 500,000 480 1 1 ½
10 600
A2-070 700,000 672 1 ¼ 1 ½
12 650
A2-097 970,000 932 1 ¼ 1 ½
16 700
A2-120 1,200,000 1152 1 ½ 1 ½
16 804
A2-140 1,400,000 1345 1 ½ 1 ½
18 944
Dimensions In Inches; GPH = Gallons Per Hour; * Approximate
** Propane Model Input Is 10% Less
INTRODUCTION

Page 4
MODEL IDENTIFICATION
The model number can be found on the Name Plate label, located on the heater/boiler.
A2 - (H,X,B,T,C) - (###) - (NG,LP,NH,LH)
A2 = A2000 Series Water Heater or Boiler
H = Water Heater
X = Water Heater with 2-Stage burner controls
B = Boiler
T = Boiler with 2-Stage burner controls
C = Boiler with ASME CSD-1 controls
### = Nominal Rated Input
NG = Natural Gas
LP = Propane
NH = Natural Gas, High Altitude
LH = Propane, High Altitude
RATINGS AND CERTIFICATIONS
The A2000 models are certified to the following standards:
•ANSI Z21.13 – CSA 4.9 Gas-Fired Hot Water Boilers, Latest Edition
•ANSI Z21.10.3 – CSA 4.3 Gas Water Heaters, Latest Edition
All A2000 models are ASME National Board Approved and are constructed in accordance with Section IV of the
ASME Heater Pressure Vessel Code (160 psi working pressure) and bears the ASME “H” stamp.
Do not alter or replace the heat exchanger without the approval of Green Boiler
Technologies. To do so will void the warranty and the ASME certification.
Ensure the fuel that the appliance will burn is the same as that specified on the boiler rating
plate. Conversions must be completed by a Qualified Service Agency or Gas Provider. Call
your Green Boiler Technologies Representative or Customer Service for instructions and the
proper conversion kit.

Page 5
 PRODUCT RECEIPT
On receipt of your heater/boiler, visually check for external damage to the appliance or shipping crate. If the
crate is damaged, make a note to that effect on the Bill of Lading before signing for the shipment. After
removing the appliance from the shipping crate, report any damage to the carrier immediately. If any items were
shipped loose, make sure they were received. All carrier claims are your responsibility.
All claims for damage or shortages must be filed with the carrier. Before product is returned, permission and an
Authorized Return Goods Number (RMA) must be acquired from the manufacturer. Product returned to the
factory without an authorized RMA will not be accepted. All returned product is subject to a restocking charge.
 HIGH ELEVATION
For units installed at elevations above 2,000 feet over sea level, consult the factory for the proper burner
orifices.
Units installed at elevations above 2,000 feet must be de-rated to account for the
lower percentage of oxygen present in the air. Personal injury due to the inhalation
of Carbon Monoxide may result if the unit input is not properly de-rated.
 INSTALLATION CODE REQUIREMENTS
1. The installation of the unit must conform to the requirements of the authority having jurisdiction or, in the
absence of such requirements, to the National Fuel Gas Code, ANSI, Z223.1 / NFPA 54, Latest Edition
and the National Electric Code (NEC) ANSI/NFPA 70.
2. Where required by authority having jurisdiction, the installation of water boilers must conform to
American Society of Mechanical Engineers Safety Code for Controls and Safety Devices for
Automatically Fired Boilers, No. CSD-1.
3. For Canada only, the installation must conform to CAN/CGA B149 and CSA C22.1 Part 1.
It is important to wear eye protection and gloves while installing, servicing or
repairing the unit. A dust respirator is recommended while servicing or repairing the
burner assembly or combustion chamber area. Use caution when working on roofs
and/or scaffolding. Proper and safe scaffolding and/or ladders must be used and all ladders should be
secured when in use. Check overhead for antennas, power lines and other obstacles before erecting
ladders or scaffolding and while working on any roof structure.
This manual must be thoroughly reviewed and understood before installing your A2000
heater/boiler. Installation and Service must be completed by a Qualified Installer, Service
Agency or Qualified Gas Supplier. If you have any questions which are not covered in the
manual, please contact Green Boiler Technologies or your local representative.
INSTALLATION

Page 6
 LOCATION & PLACEMENT
When installing the boiler or heater, consideration must be given to proper location. In addition to the following
requirements, the installation must adhere to all local or state code requirements.
1. The unit should be leveled.
2. Minimum clearance for hot water pipes and venting from combustible material is 6 inches.
3. The boiler/heater must not be installed on carpeting or other combustible flooring.
4. The unit is for alcove installation on non-combustible floors only. The minimum clearance for
combustible material:
Minimum Clearance A-035 A-050 A-070 A-097 A-120 A-140
Back & Side Walls 24 24 24 24 24 24
Top of Jacket to Ceiling 51 51 56 56 56 56
Dimensions in Inches
5. The heater/boiler must be installed so that it can be serviced without removing the heater/boiler or any
surrounding structure. The minimum space required in front of the boiler to allow removal of the burner
is:
Minimum Clearance A-035 A-050 A-070 A-097 A-120 A-140
Burner Removal 23 28 32 35 35 35
Dimensions in Inches
6. A hot water boiler installed above radiation level must be provided with a low water cutoff device either
as a part of the boiler or at the time of boiler installation.
7. The boiler/heater shall be protected from freezing. Heat exchangers damaged by freezing shall not be
considered for warranty.
8. The unit must be located where condensation or leakage from the heat exchanger or connections can
be drained and will not result in damage to the adjacent area or to lower floors of the structure. If this
cannot be avoidable, use of an adequately drained catch pan is recommended. The pan must not
restrict combustion air flow to the burner.
9. The boiler/heater must be installed such that the gas ignition system and other electrical components
are protected from water (dripping, spraying, rain, etc.) during operation and service.
Maintain the area surrounding the heater/boiler clean and free of combustible
materials, gasoline, and other flammable liquids or vapors. The heater/boiler should
never be covered.
 COMBUSTION AIR REQUIREMENTS
The boiler/heater room must be provided with TWO openings to assure adequate combustion air and proper
ventilation. One opening should be 6 to 12 inches above the floor and the other 6 to 12 inches below the ceiling,
preferably on opposite walls. The size of each opening will vary based on whether the air is taken from inside or
outside the building, and with the input rating of the boiler/heater.
The make-up air must be sized for the total BTU per hour demand of ALL gas fired or
air using appliances served by these openings.

Page 7
When air is taken directly from the outdoors or through a vertical duct, each opening must have a minimum of 1
square inch (6.5 cm
2
) per 4,000 Btu/hour. If a horizontal duct is used, each opening must have a minimum of 1
square inch per 2,000 Btu/hour is required.
When air is taken from another interior space, each opening should have a minimum free area of 1 square inch
for each 1,000 Btu/hour of gas input, but not less than 100 square inches. The area of the room the boiler is
located in, plus the area it is communicating with for combustion air, must meet the large room criteria described
in the National Fuel Gas Code.
Example 1: One 500,000 btu/hr input boiler with air taken from the outdoors through two horizontal ducts. The
open area of each duct must be at least 250 square inches (161 cm
2
). [500,000 / 2,000] = 250]
Example 2: One 350,000 and one 1,400,000 btu/hr input boilers, with air taken from the outdoors through two
vertical ducts. The open area of each duct must be at least 437.5 square inches (2823 cm
2
). [(1,400,000 +
350,000) / 4,000 = 437.5]
Provision for combustion and ventilation air must be in accordance with Section 5.3 of the National Fuel Gas
Code, ANSI Z223.1 (latest edition) or applicable provisions of the local building code.
Under no circumstances should the boiler room ever be under a negative pressure.
Particular care must be taken when steam boilers, exhaust fans, compressors, air
handling units or other equipment may rob air from the unit.
The combustion air supply must be free of chemical fumes, which may be destructively corrosive when
burned. Examples of chemicals that must be avoided are fluorocarbons and other
halogenated compounds, commonly present as refrigerants or solvents, such as
Freon, trichloroethylene, and chlorine. These chemicals, when burned, form acids that
will attack the boiler tubes, flue collectors, and boiler stack, resulting in premature boiler failure.
Canadian Installations: All combustion air must be drawn from outside the building. The mechanical
equipment room must communicate directly with the outdoors. Refer to CGA B149 Installation Code for
additional information.
 ELECTRICAL REQUIREMENTS
Installations must follow the National Electrical Code (NEC) ANSI/NFPA No. 70, latest edition (CSA C22.1 CEC
Part 1 for Canada) and any other local codes or regulations having jurisdiction. The unit must be electrically
grounded in accordance with NEC. Install a separate disconnect means for the heater/boiler.
The electrical conductors shall be type MTW 105
o
C wire, with black for hot, white for neutral, and green for
ground. All electrical wiring must be protected from mechanical damage. The conduit and junction box shall be
UL approved with the wall thickness of the steel junction box at least 0.031 inches (0.79 mm).
The A2000 water boiler/heater operates on 115V, 15 amp, 60Hz power. A transformer is provided to reduce the
voltage to 24 volts for the ignition control module and gas valve operation. Consult the wiring diagram located
on the heater/boiler or the Wiring Diagrams section of this manual for the specific connection points and control
devices applicable for your model.
ELECTRICAL SHOCK HAZARD: Ensure electrical power to the heater/boiler is disconnected before
connecting power, auxiliary controls and components or servicing.
Do not attach any electrical components to the interior or exterior of this boiler/heater
unless given authority to do so by a representative of Green Boiler Technologies.
All models are furnished with a pre-wired, manual reset, water high limit temperature switch.
This temperature switch must not be used as an operating aquastat. A separate operating
temperature controller is required for proper operation of this appliance (see wiring diagrams for suggested
location in the electrical circuit). Failure to install a separate operating temperature controller will result in short
cycling. Typically, water heaters are installed along with a storage tank and the temperature controller is

Page 8
mounted in the lower half of the storage tank. Boiler temperature controls are typically mounted in the primary
loop. If the temperature control sensor is mounted directly on the heater/boiler water piping, the sensor must be
installed on the inlet water piping to prevent short cycling of the appliance.
A water flow switch must be installed by the installer and wired to prevent the unit from firing if for any reason
there is an inadequate flow of water through the boiler/heater (see wiring diagrams for suggested location in the
electrical circuit). NOTE: CSD-1 model boilers only, are equipped with a factory installed operating
aquastat.
Optional, circulation pumps can be supplied for single or three phase and 115 to 460 volts as required. The
pump power must be wired independently and should be adequate for the amp rating of the pump motor. Refer
to the Operating Instructions and Wiring Diagrams sections of this manual for more information regarding
pumps.
 GAS REQUIREMENTS
Ensure the fuel the appliance will burn is the same as that specified on the boiler
rating plate. Conversions must be completed by a Qualified Service Agency or Gas
Provider. Call your Green Boiler Technologies Representative or Customer Service
for instructions and the proper conversion kit.
The gas supply meter, regulator, and piping must have sufficient capacity to supply all gas fired appliances they
feed without undue pressure loss. If the gas meter, regulator or piping is too small, request the gas company
install equipment with adequate capacity.
The allowable pressure loss in gas piping between the gas meter or service regulator and each appliance is
generally between 0.3 to 0.5 inches of water column. Refer to the National Fuel Gas Code, ANSI Z223.1, Latest
Edition, for sizing guidelines.
Example: For 20 equivalent feet of 1-1/2 inch piping, the maximum cuft/hr gas flow with a 0.3 inch w.c.
pressure loss is 726. For natural gas at 1025 Btu/cuft, the maximum firing rate is 744,000 Btu/hr
[726 x1025]. For propane at 2500 Btu/cuft, the maximum firing rate is 1,815,000 Btu/hr [726 x
2500].
Maximum and minimum gas pressure delivered to the boiler/heater is shown below. If the gas supply line
pressure is greater than the maximum listed, a pressure regulator must be installed at least 10 pipe diameters
upstream of the boiler/heater.
Max Length
(Equivalent feet)
3/4
1
1-1/4
1-1/2
2
2-1/2
3
4
10
273
514
1060
1580
3050
4860
8580
17500
20
188
353
726
1090
2090
3340
5900
12000
30
151
284
583
873
1680
2680
4740
9660
40
129
243
499
747
1440
2290
4050
8270
50
114
215
442
662
1280
2030
3590
7330
60
104
195
400
600
1160
1840
3260
6640
70
95
179
368
552
1060
1690
3000
6110
80
89
167
343
514
989
1580
2790
5680
90
83
157
322
482
928
1480
2610
5330
100
79
148
304
455
877
1400
2470
5040
125
70
131
269
403
777
1240
2190
4460
150
63
119
244
366
704
1120
1980
4050
175
58
109
224
336
648
1030
1820
3720
200
54
102
209
313
602
960
1700
3460
Gas Pipe Sizing Chart: Cubic Feet of Gas Per Hour
ize chedule 40 Metallic Pipe (inches)
Ta ble Val ues For Na tura l Ga s , pecifi c Gra vity 0.60
Typical Natural Gas = 1025 Btu per cuft ; Typical Propane = 2,500 btu/cuft

Page 9
Maximum Pressure Minimum Pressure
Natural Gas 9 5
Propane 15 13
Units: Inches of Water
The A2000 series water boiler/heater is not intended to operate at a gas supply
pressure other than shown on the rating plate. Exposure to a higher gas supply
pressure may cause damage to the gas valves, which can result in fire or explosion.
The gas supply piping must have a 3 inch (7.6 cm) minimum sediment trap
(sometimes referred to as a dirt trap or drip leg) and a manual shut off valve
ahead of the boiler/heater. The sediment trap should be located as close to the
heater as possible, be readily accessible and not subject to freezing conditions. A
union of the ground joint or flanged joint type must be installed in the gas supply
piping adjacent to the boiler/heater for ease of service.
It is important to guard against gas valve fouling from
contaminants in the gas piping. Fouling may cause
improper operation, fire or explosion. Clean the inside of
all supply pipe and fittings prior to insulation. Do not use Teflon tape. Use
only a joint compound suitable for natural gas and propane. Apply the joint
compound sparingly, only on the male threads and do not apply to the first
two threads.
To prevent damage, do not apply excessive torque when attaching the gas supply line
to the boiler/heater gas valve.
The gas supply piping must be adequately supported by using hangers or other suitable types of support. Do
not use the boiler/heater gas train to support the gas supply piping.
The boiler/heater and its gas connections must be leak tested prior to placing the unit in operation. Use soap
and water solutions or other material acceptable for the purpose of locating gas leaks. Do not use matches,
candles, flame, or other sources of ignition for this purpose.
During pressure testing, disconnect the heater/boiler from the gas supply if the test pressure is equal to or
greater than ½ psig (3.5 kPa). The gas supply line must be capped when not connected to the boiler during this
process. Relieve the gas pressure in the gas supply line prior to re-connecting to the boiler/heater. Failure to
follow this process may damage the gas valves and voids the warranty on the gas valves.
Do not subject the boiler/heater gas train components to pressures equal to or greater
than ½ psig. Damage to the gas valves may result.
Local codes may require the vents on the supply regulators and safety vent valves be piped to the outside.
When required, this piping is part of the gas supply piping and not part of the boiler/heater. It is important to
insure these vents are protected against blockage, with special care given to prevent blockage from rain,
condensation, ice, or snow.
When multiple appliances are fed gas from the same supply line, individual point of use regulators are
recommended to minimize variations in supply pressure.

Page 10
 WATER CONNECTIONS
The type of system in which the boiler/heater is to be used will determine the type of water connections to be
made. Consult the piping schematics provided in the DIAGRAMS section before beginning the installation. Be
sure to install the unit in accordance with the installation instructions to insure proper operation and safety.
The heater/boiler should be located so that any water leaks will not cause damage to the adjacent area or
structures. If this cannot be avoided, use of a properly sized, drained catch pan is recommended. The catch
pan must not impair combustion air flow to the burner. Union connections and shut off valves must be provided
at the unit to facilitate future service which may be required.
The ASME pressure relief valve supplied on the unit must be piped to a drain or to a safe location to prevent
accidental burns should the valve discharge hot water. DO NOT install a valve between the relief valve and the
heater. DO NOT install reducing coupling, restriction, or valve in the relief valve discharge line. DO NOT pipe
to an area where freezing could occur. Local code requirements concerning size, type and placement of other
safety valves must be followed. The relief valve should be checked at least once yearly by manually operating
the release lever to insure proper operation.
A discharge line must be connected to the pressure relief valve and piped to a safe
location. Do Not Install a valve or other restriction between the relief valve and
heater, or the relief valve and the end of the discharge line. Water discharging from
the relief valve will be very hot and may cause series injury.
If the heater/boiler is connected to a water storage tank, a temperature and pressure relief valve must be
installed on the tank. The temperature/pressure relief valve serves as a safety device to prevent excessive
pressure and temperature. Excessive pressure may be caused by the expansion of water when it is heated in a
closed system. A closed system is one that has a check valve, back-flow-preventer, or a pressure-reducing
valve in the cold water supply line. In this type of system it is normal for the relief valve to relieve small
quantities of water from the closed system when the boiler is firing and no water is being used. An expansion
tank or other suitable means must be provided to control thermal expansion.
Insulating or dielectric unions or bushings should be used in connections between dissimilar metal fittings (such
as between copper and galvanized). These fittings are required to minimize electrolytic corrosion, which can
result from direct connection of dissimilar metals in a water system.
A flow switch must be installed and wired to prevent the unit from firing if there is an inadequate flow of water
through the boiler/heater. A flow switch on this unit meets CSD-1 safety requirements as a low water cut-off
device. Note: A factory-wired flow switch is provided on all CSD-1 models. The flow switch should be set
so that the heater/boiler will not fire when the flow rate is less than that which will provide greater than a 80
o
F
(44
o
C) temperature rise through the heater/boiler.
When used for both potable water heating and space heating, all piping and components connected to the
system for space heating must also be suitable for use with potable water. Do not introduce toxic chemicals,
such as those used for boiler treatment, into the system. Any components previously used with non-potable
water must not be connected to the potable water system.
Flow Switch
deg F deg C A2-035 A2-050 A2-0 0 A2-09 A2-120 A2-140
80 44 7.0 10.0 14 19 24 28
0 39 8.0 11 16 22 28 32
60 33 9.4 13 19 26 32 37
50 28 11 16 22 31 39 45
40 22 14 20 28 39 48 56
30 1 19 27 37 52
20 11 28 40 56
A2000 Model
Flow Rate (gpm) Vs. Water Temperature Rise
Recommended Temperature Rise: 20 - 45
o
F
Temp Rise

Page 11
When the system requires water for space heating at temperatures higher than 140
o
F (60
o
C), use a mixing
valve or similar means to reduce the potable water supply temperature to avoid scald injuries. The operating
thermostat should be set at the lowest possible temperature that provides useful service for the application. For
potable water uses, 120 – 125
o
F (49 – 51
o
C) is recommended (use a tank mounted Operating Aquastat).
This heater/boiler requires forced water circulation when the burner is operating. Pump selection and sizing
depends upon the type of system in which the heater/boiler will be used. Pressure loss through the A2000 heat
exchanger is provided below. The maximum flow rate through the A2000 heat exchanger is 56 gpm due to
velocity induced tube erosion.
The A2000 models are designed to operate with a return water temperature of 120
o
F (49
o
C) or greater.
Condensation of the flue gasses may result if the inlet water temperature is under 120° F. This appliance and
the venting connected to it are not designed to withstand repeated condensation. Low operating temperatures
and frequent cold start-ups must be prevented. Frequent operation below 120°F return water temperature will
damage the heat exchanger and void the warranty. If low operating temperatures cannot be avoided, a
feedback loop (by-pass) must be installed as shown in the DIAGRAMS section.
Do not operate your A2000 heater/boiler with inlet water temperatures lower than
120
o
F (49
o
C). Consistent operation below these temperatures will cause heat
exchanger corrosion and void the warranty. A By-Pass piping arrangement is
required when inlet water temperatures are consistently below 120
o
F.
Water temperature thermometers should be obtained and field installed as shown in the DIAGRAMS section.
Water Chemistry: Water that is very soft, very hard, having a high total dissolved solids (TDS), or an acidic or
alkaline pH will shorten the life of the heat exchanger. The water should be between 5 and 15 grains per gallon
hardness. Water with a hardness exceeding 15 grains or a TDS exceeding 2500 ppm should be softened or
treated to prevent scaling of the heat exchanger, which reduces efficiency and ultimately may cause premature
failure of the heat exchanger due to overheating. Water softer than 5 grains may be corrosive, causing
premature heat exchanger failure, and must be treated with a suitable buffer. The ideal pH for water used in a
storage tank or copper heating system is 7.2 to 7.8. Corrosion of the heat exchanger may result when the pH is
lower than 6 or higher than 8.
Scaling of the heat exchanger is aggravated with low water flow rates and high water temperatures. To
minimize scaling, use the highest water flow rate and lowest water temperature set-point suitable for the
application.
FAILURE TO PROPERLY OBSERVE THE ABOVE WATER CHEMISTRY
RECOMMENDATIONS WILL VOID THE WARRANTY AND MAY RESULT IN A VERY
SHORT LIFE OF YOUR BOILER/HEATER.
Leak Testing: The A2000 heater/boiler does not require hydrostatic pressure testing, as the heat exchanger
was factory tested for 160 psig operating pressure. However, the water piping connections to the heater, and
the balance of the water system should be leak tested prior to putting the system into operation. Leaks must be
immediately repaired to prevent damage to the heater or property.
Flow
(gpm) A2-035 A2-050 A2-0 0 A2-09 A2-120 A2-140
10 1.5 2.0 2.5 4.5 4.5 4.5
20 4 6 8 12 12 12
30 9 13 15 21 21 21
40 17 22.5 26 35 35 35
50 36 46 52 52 52
56 57 64 64 64
Head Loss (ft hd) Vs. Water Flow Rate Through Heat Exchanger (Approximate)
A2000 Model
psi = (ft hd) x 0.434

Page 12
When a boiler is used in connection with refrigeration systems, it must be installed so
the chilled medium is piped in parallel with the heating boiler with appropriate valves
to prevent the chilled medium from entering the boiler. When a boiler is connected to
heating coils located in air handling units where they may be exposed to refrigerated air circulation, it
must be equipped with flow control valves or other automatic means to prevent gravity circulation of the
boiler water during the cycle.
IMPORTANT: Before attempting to start the unit, be sure the system is full and the water is free to flow through
the unit. All air must be relieved from the unit and piping and the pump must be working before the unit is fired.
 VENTING SYSTEM
Proper installation of the flue venting is critical for the safe and efficient operation of
your heater/boiler. Failure to conform with any of these requirements may violate
local, state or federal codes as well as create conditions that may cause catastrophic
property damage or personal injury.
The venting system must comply with the National Fuel Gas Code, ANSI, Z223.1 / NFPA 54, Latest Edition, or
for Canada, CAN/CGA B149.1, and all local codes. Venting must be provided to completely remove all gases
and products of combustion to the outside, without condensation in the stack or spillage at the draft hood.
The A2000 heater/boilers are negative vent, non-condensing Category I appliances and can utilize un-insulated
single wall “B” vent connectors. Vent material must be listed by a nationally recognized test agency. Insulated
metal vent pipe must be used for outdoor vent sections in cold climates to reduce condensation. Observe
clearances in accordance with applicable codes from all combustible materials. Use insulated venting or vent
pipe spacers where the vent passes through combustible roofs, floors, and walls.
Natural draft vent systems utilize natural buoyancy of the hot flue products to create the pressure difference that
allows the flue products to exhaust from the flue. The negative pressure draft should be -0.1 to -0.8 inches of
water column when measured 12 inches (30 cm) above the draft hood to ensure proper operation.
Do not reduce the vent diameter and avoid sharp turns in the vent piping. Use the same size stack and draft
diverter as the discharge from the unit. The vent sizes for A-2000 models are:
Model: A2-035 A2-050 A2-070 A2-097 A2-120 A2-140
Vent Diameter 9” 10” 12” 16” 16” 18”
The draft hood that was supplied with you’re A-2000 model must be installed
directly on top of the unit. The draft hood slips over the flue outlet flange.
General Venting Requirements:
•The maximum and minimum vent length for Category I systems is
determined by the National Fuel Gas Code, or for Canada, B149.
•Avoid long horizontal runs of vent pipe, reductions, restrictions, and 90
o
elbows. The length of the horizontal run should be as short as possible,
but must not exceed 75% of chimney height.
•All horizontal runs must slope upward toward the termination at least ¼ inch per foot (2 cm per meter)
and be adequately supported.
•A2000 models are designed to operate with a negative pressure in the exhaust venting. This appliance
is NOT approved for side-wall venting. Consult your GBT representative or Customer Service if side-
wall venting is required.
•When any horizontal vent extends for more than 6 feet (1.8 meter), vent supports must be installed with
Draft Ho
od

Page 13
subsequent supports after every additional 6 feet. The support must be secured using at least #10
fasteners to a solid material (solid masonry or wood framing or blocking). Do not fasten to drywall
sheathing using hollow wall anchors. As an alternative, a threaded rod and trapeze support in
accordance with SMACNA HVAC Construction Standards – Metal and Flexible, latest edition, shall be
installed every 6 feet of continuous horizontal vent and after any offset elbows.
•Install an approved cap for the stack outlet. The bottom of the cap must be one stack diameter above
the top of the stack and so designed to prevent snow or any debris from blocking the vent. The top of
the stack must be carried to a minimum of two feet above the highest point of the roof or any other
obstructions within 8 feet (2.4 meter) of the termination. The vent must not terminate near an air supply
inlet to any building.
•The venting system must be planned so as to avoid possible contact with concealed plumbing or
electrical wiring inside the walls.
•Venting in a multi-family structure must be enclosed when passing through occupied or unoccupied
spaces above the connected boiler. The enclosure is to be of materials no less fire resistant than
surrounding floors and walls. It is recommended that the system be enclosed whenever passing through
occupied spaces. Be sure to check your local building codes for additional requirements.
•Minimum clearance of 4 feet (1.2 meter) (6 feet or 1.8 meter in Canada) horizontally must be maintained
between the unit and vent stack from electric meters, gas meters, regulators and relief equipment (no
part of the unit or venting may be directly above or below electric meters, gas meters, or regulators).
•A vertical support must be installed at least twice in any continuous vertical run, or every 10 feet. Install
a Vent Roof Jack Assembly or Fire stop Plate at every penetration of a floor or ceiling.
•Roof Line: The vent system must terminate at least 3 feet (0.9 meter) and no more than 6 feet (1.8
meter) above the roof line, and no closer than 8 feet (2.4 meter) from any wall or vertical structure.
Vents extending above the roof more than 5 feet (1.5 meter) should be secured using guy wires or
braces to withstand wind or snow loads.
These units are engineered for natural draft and may not be connected into any
portion of a mechanical or other draft system operating under positive pressure.
Verify that the venting is under negative pressure when all boiler room doors are
closed, the heater/boiler is firing, and all other air using appliances in the room are operating. If the
venting is under positive pressure during operation a draft inducer must be installed, vent material
suitable for positive pressure must be installed and all joints must be sealed.
Common Vent System: Manifolds that connect more than one heater/boiler to a common chimney must be
sized to handle the combined load. At no time should the area of the common vent be less than the area of the
largest heater/boiler exhaust outlet.
Common vent systems may be too large if an existing unit is removed. When an
existing appliance is removed, the vent system design must be carefully evaluated
for proper sizing (Refer to MAINTENANCE Section of this manual).

Page 14
Follow these instructions exactly. A fire or explosion may result, potentially causing
personal injury, loss of life and property damage.
Do not use this appliance if any part has been flooded or heavily sprayed with water.
Immediately call a qualified service technician to inspect the controls and replace any
part that has been damaged by water.
 PRE-START CHECKLIST
Before starting the boiler, review the following:
•Is the unit properly sized for the application?
•Is the gas supply properly sized and installed?
•Is the vent system properly installed?
•Is the combustion and ventilation air adequate?
•Is the water system properly installed and filled with water?
•Is the proper operation understood and all instructions followed?
This appliance is equipped with an ignition device, which automatically lights the
burner. DO NOT TRY TO LIGHT THE BURNER BY HAND.
 FILL THE SYSTEM WITH WATER.
Fill the system with water and purge all air. Trapped air can prevent proper water circulation. Check the water
piping system for leaks and if found, repair immediately.
 PURGE AIR FROM GAS LINES
For a new installation, or if the gas lines feeding the heater/boiler were opened to the atmosphere during
installation or service, air in the gas lines must be purged before operating the unit.
Before purging gas lines, ensure electrical power is turned off to the heater/boiler AND ALL OTHER
APPLIANCES IN THE VICINITY OR ROOM. TURN OFF GAS TO ALL APPLIANCES IN THE VICINITY OR
ROOM.
Provide ventilation from the area around the heater/boiler to the outdoors, preferably using
a fan or blower.
Loosen the pipe union or fitting upstream and adjacent to the heater/boiler. Slowly, partially open the manual
gas valve installed upstream of the loosened union or connection. Allow the trapped air to exit the gas piping
until the smell of gas is noticed. Close the manual gas valve and reconnect the pipe union or fitting. Wait at
least 15 minutes before turning electrical power back and/or gas back on to the other appliances, and only after
you are sure purged gases have dissipated.
 PREPARATION
1. Ensure the manual gas valve upstream of the heater/boiler is CLOSED.
2. For A2-035 and A2-050 models, ensure the main regulating gas valve is closed.
Before turning on the power to this appliance smell all around the appliance for gas. Be sure to smell
next to the floor because some gas is heavier than air and will collect near the floor.
START-UP & OPERATION

Page 15
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. Follow the gas supplier’s instructions.
•If you cannot reach your gas supplier, call the fire department.
3. Turn on electrical power to the heater/boiler. Using a multi-meter, check voltage between the HOT and
COMMON (should be about 120 Volts).
4. Check voltage between the HOT and Ground (should be about 120 Volts).
5. Check voltage between the COMMON and Ground (should be less than 1 Volt).
If the COMMON – Ground is more than 1 Volt, STOP! Contact a licensed electrician to
correct the ground fault.
6. Turn OFF electrical power to the heater/boiler.
7. Attach 24 inch manometers to the gas line so that the gas pressure can be measured upstream of the
first heater/boiler automatic gas valve, downstream of the last automatic gas valve, and between
automatic gas valves. NOTE: Depending upon the model, your heater/boiler may be equipped
with one or two automatic gas valves.
8. Install water temperature measurement thermometers in the water inlet and outlet piping.
9. Slowly turn on the manual gas shut off valve upstream of the heater/boiler.
10. Read the gas supply pressure using the manometer. Verify that the supply gas supply pressure is
between the minimum and maximum per the table below. If the pressure is not within these limits,
check to see if a service gas regulator is installed and adjust accordingly.
Maximum Pressure Minimum Pressure
Natural Gas 9 5
Propane 15 13
Units: Inches of Water
Do not operate heater/boiler if the gas supply pressure is not within the limits shown
in the table above.
11. Turn OFF the manual gas shut off valve upstream of the heater/boiler.
12. Turn ON electrical power to the heater/boiler ON.
13. Turn the operating thermostat to a setting high enough to turn on the water pump. Verify water is
flowing though the heater/boiler by verifying the flow switch has closed.
Manual Gas Shut-Off Valve, All Other
Models
A2-(H,B) 035/050 Main Regulating Gas Valve

Page 16
14. Turn the operating thermostat to its lowest setting so that water pump stops.
 START-UP
1. Slowly turn on the manual gas valve upstream of the heater/boiler. For A2-035 and 050 models only,
turn on the manual valve located on top of the Robertshaw automatic gas valve.
2. Turn the operating thermostat to a setting high enough to turn on the water pump.
3. The ignition control module will turn on the spark ignition system and pilot operating valve to light the
pilot burner. If the pilot does not light the first time, it will retry, up to three times. This is normal during
the initial start-up due to air in the pilot line. If, after trying three times, the pilot burner does not light,
remove power to the ignition module to reset, by either turning the operating thermostat down to its
lowest setting or turning off electrical power to the heater/boiler.
NOTE: CSD-1 models only utilize an ignition module that waits 5 minutes before attempting to
re-light the pilot.
4. After the pilot burner is lit and pilot flame is proven, the Ignition Module will open the automatic main gas
valve(s) and the main burner will light.
If the pilot or main burner fails to light after repeated attempts, shut off the
manual gas valve upstream of the heater/boiler, remove electrical power from
the heater/boiler, and call your qualified service technician or gas supplier.
5. Check for gas leaks in the gas train assembly using soap and water or an appropriate leak check fluid.
DO NOT use an open flame to check for gas leaks.
6. Using the manometers with the heater/boiler operating, check to make sure the gas supply pressure is
within the limits shown above.
7. Check the manifold gas pressure downstream of the automatic gas valves using the outlet pressure tap
provided on the gas valve (A2-035 and 050 models only) or the pressure tap provided in the gas piping.
•For Natural Gas models, the manifold pressure should be set to 4.0” water column.
•For Propane Gas models, the manifold pressure should be set to 10.5” water column.
•For 2-Stage models, see the Operating Section for setting the gas manifold pressure.
a. For A2-035 and A2-050 models, adjust the manifold pressure using the adjustment screw
located on top of the Robertshaw gas valve (remove the dust cover cap to expose the
adjustment screw).
b. For A2-070, 970, 120 and 140 models, adjust the manifold pressure using the Maxitrol gas
pressure regulator located upstream of the automatic gas valve (remove the dust cover cap to
expose the adjustment screw).
c. Replace the manifold pressure adjustment screw caps
8. With the manifold gas pressure set per step 6 above, observe the main burner flame characteristics.
The burner flame should be blue at the base, with yellow at the tips permissible. An excessive amount
of yellow flame suggests a lack of combustion air or inadequate vent draw.

Page 17
9. Verify the water flow switch opens at the minimum water flow rate by slowly closing a manual ball valve
installed in the water outlet piping, until the difference between the water inlet and outlet reaches 95 –
100
o
F (53 – 55
o
C). Note: The operating thermostat may have to be turned to its highest setting in
order to conduct this test. If the main burner does not shut down when this temperature difference is
achieved, adjust the flow switch set point until the flow switch opens (refer to Operating Section for
instructions concerning setting the flow switch).
10. Fully open the manual ball valve in the water outlet piping.
11. After the main burner has been in operation for at least five (5) minutes, inspect the venting for spillage.
Draft tests must be done with the appliance firing. Proper draft or airflow in the venting may be
determined by either of the following means:
oSmoke Test – Place a source of smoke or other visible fumes under the opening of the draft
hood. If the fumes are all drawn up the draft hood opening, the appliance is drafting properly. If
any fumes roll outside of the vent hood there is a problem with the drafting or make-up air.
oDraft Gauge – A draft pressure gauge can be inserted into the vent pipe directly above the draft
hood. The draft gauge must show a constant negative pressure.
12. Turn the operating thermostat down to its lowest setting. The pilot and main burner will shut off. Close
the manual gas valve immediately upstream of the heater/boiler.
13. Remove the gas pressure manometers and replace all plugs. Use an appropriate pipe thread sealant
(do not use Teflon tape).
14. Open the manual gas valve immediately upstream of the heater/boiler and set the operating thermostat
at the desired temperature.
NOTE: Low inlet water temperatures on start-up may create flue gas condensation which may
gather on the floor under the heater. THIS IS NOT A LEAK. The unit will stop condensating when it
reaches standard operating temperatures.
 SHUT DOWN PROCEDURE
1. Set the operating thermostat to lowest setting and turn the gas valve to “OFF.”
oFor A2-(H,B)-035/050 models, rotating the control knob on top of the combination regulating gas
valve to the “OFF” position turns off the gas.
oFor all other models, the gas is turned off by rotating the handle on the separate manual gas
valve to a position perpendicular to the gas piping.
2. Switch off all electrical power to the system.
Main Burner Flame Pilot Burner Flame

Page 18
 OPERATION
The A2000 models are simple ON/OFF water heater/boilers. The units are turned ON and OFF by the
application or removal of 120 VAC power to the control panel. Normally, this 120 VAC power is provided
through an operating thermostat. Safety controls (such as a flow switch and manual reset water high limit
temperature switch) installed between the operating thermostat and the heater/boiler prevent power from
reaching the control panel if water flow is not present, or the outlet water temperature has been exceeded.
When 120 VAC power is applied to the heater/boiler control panel on a call for heat from the operating
thermostat, 24 VAC is applied to the Ignition Control Module via a transformer. The ICM provides spark to the
igniter, opens the pilot burner operating valve providing gas flow to the pilot burner, and looks for flame
verification through the spark igniter electronics. Once pilot flame is verified, the ICM opens the automatic main
burner valve(s), which provides gas flow to the main burner, which is ignited by the pilot burner.
If the pilot flame is not verified, the ICM will try to light the pilot burner two
more times (see CSD-1 Section below for control differences specific to
CSD-1 models). After the third try, the ICM will go into lock-out. The ICM
can be reset by removing power to the heater/boiler. The pilot burner
remains ON the entire time the main burner is ON. If pilot flame verification
is lost while the main burner valves are ON, the ICM will close the main
burner valves and try to re-establish pilot burner flame.
When the operating thermostat is satisfied, the 120 VAC is removed, and the
normally closed pilot valve and main burner valves close.
Operating Thermostat Setting: A separate operating temperature controller is required for proper operation of
this appliance. Failure to install a separate operating temperature controller will result in short cycling. Water
heaters are expected to operate at temperatures between 120 °F and 155 °F (49 to 68
o
C) Water boilers can
operate with return water temperature up to 190 °F (88
o
C) and a supply temperature up to 240
o
F (115
o
C).
Return water temperatures must be kept above 120 °F to prevent condensation. Refer to the DIAGRAMS
section for recommended piping for lower operating water temperatures. Frequent operation below 120°F (49
o
C) return water temperature will damage the heat exchanger and void the warranty.
Do not operate your A2000 heater/boiler with return water temperatures lower than
120
o
F (49
0
C). Consistent operation below these temperatures will cause heat
exchanger corrosion and void the warranty.
When the heater/boiler is used for potable water heating, use a
mixing valve or similar means to reduce the potable water
supply temperature to avoid scald injuries. The mixing valve
should be set at the lowest possible temperature that provides
useful service for the application. For potable water uses, 120
– 125
o
F (49 – 51
o
C) is recommended.
Water temperatures higher than 125
o
F
(51
o
C) can cause severe burns,
personal injury or loss of life. The
temperature at which injury occurs
varies with a persons age and the time of exposure. Never
allow small children to use a hot water tap or draw their
own bath water.
Water High Limit Switch: Every A2000 model is equipped with a manual reset, High Limit Switch on the hot
water outlet. For water heater models, the high limit has a factory stop of 200
o
F (93
o
C). For boiler models, the
factory stop is set at 240
o
F (115
o
C). The high limit switch must always be present and must never be by-
passed. If the High Limit Switch trips, it must be manually reset by pressing the red button, located on the front
cover of the High Limit Switch.
deg F deg C
> 1 0 >
160 1
150 65
140 60
130 54
120 49
Water Temperature - Scald Relationship
Water Time to Produce
Temperature 2nd & 3rd Degree
Burns on Adult Skin
Nearly Instantaneous
About 1/2 Second
About 1-1/2 Second
Less Than 5 Seconds
About 30 Seconds
More Than 5 Minutes
Ignition Control Module (ICM)

Page 19
Gas Pressure Regulator: A gas pressure regulator is provided on all A2000 water heater/boilers. This regulator
is preset at 4 inches water column for natural gas or 10.5 inches water column for Propane gas. For
A2(H,B)035/050 models, the pressure may be adjusted using the adjustment screw located on the combination
gas valve (see Figure on page 16). For all other models, except 2-Stage, a Maxitrol gas pressure regulator is
provided. If a pressure adjustment is required, remove plug and turn screw clockwise to increase pressure,
counterclockwise to decrease pressure. One complete turn will change the pressure approximately ¼ inch of
water column. For 2-Stage models, see the Items Specific to 2-Stage Models below.
Operation of the A2000 heater/boiler at gas manifold pressures greater than 4.0” w.c.
for Natural Gas, and 10.5” w.c. for Propane Gas, will cause the unit to be over-fired,
which may cause premature heat exchanger failure, serious injury, or loss of life.
Flow Switch: A flow switch is required to be installed in the outlet water line, wired so that the heater/boiler will
not fire unless the minimum water flow through the heat exchanger is present. The minimum flow rate for each
model the flow that will provide a 100
o
F (55
o
C) temperature rise through the heat exchanger (see table in
INSTALLATION Section). The set point for the flow switch can be
changed using the adjustment screw located under the electrical house
cover of the switch. Rotate the screw clockwise to increase the flow
set point, counter-clockwise to decrease the flow set point. With the
heater/boiler firing (make sure 2-Stage models are firing on HIGH),
slowly close the manual valve in the water outlet piping, until the
temperature rise through the heat exchanger approaches 100 °F (or
lower based on specific installation or requirements). Adjust the switch
set point so that the switch opens at this flow rate. Slowly open the
water valve so that the switch closes, then repeat the process to
ensure the switch is set correctly.
Risk of electrical shock. Be careful not to touch live electrical parts or bare wires
inside the flow switch housing. The voltage to the flow switch is 120 VAC.
Water Pump: All A2000 models require forced circulation of the water through the heat exchanger. Selection
and installation method of the pump depends upon the design of the system and intended use (see DIAGRAMS
section for water pump location suggestions). The pump electrical power must be wired independently and
should be adequate for the amp rating of the pump motor. Refer to the INSTALLATION section for pressure
losses through the A2000 heat exchangers. The maximum flow rate through the A2000 heat exchanger is
56 gpm due to velocity induced tube erosion. A list of acceptable water pumps and manufacturers for
the A2000 models is listed on the following page.
Water High Limit Switch –
Manual Reset
Maxitrol Gas Pressure Regulator