AER GF-116 Guide

Printed in U.S.A. REVISED JANUARY, 2009
GF-116
Instruction
No.
AERCO INTERNATIONAL, Inc., Northvale, New Jersey, 07647 USA
Installation, Operation
& Maintenance Instructions
Benchmark 3.0LN
Series
Gas Fired
Low NOx
Boiler System
Condensing, Modulating
Forced Draft, Hot Water Boiler
3,000,000 BTU/H Input
Applicable for Serial Numbers G-06-1069 and above

Telephone Support
Direct to AERCO Technical Support
(8 to 5 pm EST, Monday through Friday):
1-800-526-0288
The information contained in this
installation, operation and mainte-
nance manual is subject to
change without notice from
AERCO International, Inc.
AERCO makes no warranty of any
kind with respect to this material,
including but not limited to implied
warranties of merchantability and
fitness for a particular application.
AERCO International is not liable
for errors appearing in this
manual. Nor for incidental or
consequential damages occurring
in connection with the furnishing,
performance, or use of this
material.
AERCO International, Inc.
159 Paris Avenue
Northvale, NJ 07647-0128
www.aerco,com
© AERCO International, Inc., 2009

CONTENTS
i
GF-116 - AERCO BENCHMARK 3.0LN GAS FIRED LOW NOx BOILER
Operating & Maintenance Instructions
FOREWORD A
Chapter 1 – SAFETY PRECAUTIONS 1-1
Para. Subject Page
1-1 Warnings & Cautions 1-1
1-2 Emergency Shutdown 1-2
Para. Subject Page
1-3 Prolonged Shutdown 1-2
Chapter 2 – INSTALLATION 2-1
Para. Subject Page
2.1 Introduction 2-1
2.2 Receiving the Unit 2-1
2.3 Unpacking 2-1
2.4 Site Preparation 2-1
2.5 Supply and Return Piping 2-3
2.6 Condensate Drains 2-3
2.7 Gas Supply Piping 2-5
2.8 AC Electrical Power Wiring 2-6
Para. Subject Page
2.9 Modes of Operation and Field
Control Wiring
2-7
2.10 I/O Box Connections 2-8
2.11 Auxiliary Relay Contacts 2-10
2.12 Flue Gas Vent Installation 2-10
2.13 Combustion Air 2-10
Chapter 3 – CONTROL PANEL COMPONENTS AND
OPERATING PROCEDURES 3-1
Para. Subject Page
3.1 Introduction 3-1
3.2 Control Panel Description 3-1
3.3 Control Panel Menus 3-4
3.4 Operating Menu 3-5
3.5 Setup Menu 3-5
Para. Subject Page
3.6 Configuration Menu 3-6
3.7 Tuning Menu 3-7
3.8 Start Sequence 3-7
3.9 Start/Stop Levels 3-9
Chapter 4 – INITIAL START-UP 4-1
Para. Subject Page
4.1 Initial Startup Requirements 4-1
4.2 Tools and Instruments for
Combustion Calibration
4-1
4.3 Natural Gas Combustion
Calibration
4-2
Para. Subject Page
4.4 Unit Reassembly 4-5
4.5 Over-Temperature Limit Switch 4-5

CONTENTS
ii
Chapter 5 – MODE OF OPERATION 5-1
Para. Subject Page
5.1 Introduction 5-1
5.2 Indoor/Outdoor Reset Mode 5-1
5.3 Constant Setpoint Mode 5-2
5.4 Remote Setpoint Mode 5-2
5.5 Direct Drive Modes 5-3
Para. Subject Page
5.6 Boiler Management System
(BMS)
5-4
5.7 Combination Control System
(CCS)
5-5
Chapter 6 – SAFETY DEVICE TESTING PROCEDURES 6-1
Para. Subject Page
6.1 Testing of Safety Devices 6-1
6.2 Low Gas Pressure Fault Test 6-1
6.3 High Gas Pressure Test 6-2
6.4 Low Water Level Fault Test 6-2
6.5 Water Temperature Fault Test 6-2
6.6 Interlock Tests 6-3
6.7 Flame Fault Test 6-3
Para. Subject Page
6.8 Air Flow Fault Test 6-4
6.9 SSOV Proof of Closure Switch 6-4
6.10 Purge Switch Open During
Purge
6-5
6.11 Ignition Switch Open During
Ignition
6-5
6.12 Safety Pressure Relief Valve
Test
6-6
Chapter 7 – MAINTENANCE REQUIREMENTS 7-1
Para. Subject Page
7.1 Maintenance Schedule 7-1
7.2 Spark Ignitor 7-1
7.3 Flame Detector 7-2
7.4 Combustion Calibration 7-2
7.5 Safety Device Testing 7-3
7.6 Burner 7-3
Para. Subject Page
7.7 Condensate Drain Trap 7-4
7.8 Shutting the Boiler Down For An
Extended Period of Time
7-5
7.9 Placing The Boiler Back In
Service After A Prolonged
Shutdown
7-5
Chapter 8 – TROUBLESHOOTING GUIDE 8-1
Para. Subject Page
8.1 Introduction 8-1
Para. Subject Page

CONTENTS
iii
APPENDICES
App Subject Page
A Boiler Menu Item Descriptions A-1
B Startup, Status and Fault
Messages
B-1
C Temperature Sensor Resistance
Chart
C-1
D Indoor/Outdoor Reset Ratio
Charts
D-1
E Boiler Default Settings E-1
F Dimensional and Part Drawings F-1
App Subject Page
G Piping Drawings G-1
H Wiring Schematics H-1
I Recommended Periodic Testing
Checklist
I-1
J Benchmark Control Panel Views J-1
K Natural Gas Combustion
Calibration Procedure for Unit
SerialNos. Below G-07-1901
K-1
WARRANTIES W-1

FOREWORD
A
Foreword
The AERCO Benchmark 3.0LN Boiler is a modulating unit. It represents a true industry advance
that meets the needs of today's energy and environmental concerns. Designed for application
in any closed loop hydronic system, the Benchmark's modulating capability relates energy input
directly to fluctuating system loads. The Benchmark 3.0, with its 15:1 turn down ratio and
condensing capability, provides extremely high efficiencies and makes it ideally suited for
modern low temperature, as well as, conventional heating systems.
The Benchmark 3.0 operates at inputs ranging from 200,000 BTU/hr. to 3,000,000 BTU/hr. The
output of the boiler is a function of the unit’s firing rate and return water temperature. Output
ranges from 198,000 BTU/hr. to 2,900,000 BTU/hr., depending on operating conditions.
When installed and operated in accordance with this Instruction Manual, the Benchmark 3.0
Boiler complies with the NOx emission standards outlined in:
•South Coast Air Quality Management District (SCAQMD), Rule 1146.1
Whether used in singular or modular arrangements, the Benchmark 3.0 offers the maximum
flexibility in venting with minimum installation space requirements. The Benchmark's advanced
electronics are available in several selectable modes of operation offering the most efficient
operating methods and energy management system integration.
For service or parts, contact your local sales representative or AERCO INTERNATIONAL.
NAME:
ORGANIZATION:
ADDRESS:
TELEPHONE:
INSTALLATION DATE: _____________________________________________

SAFETY PRECAUTIONS
1-1
CHAPTER 1 SAFETY PRECAUTIONS
1.1 WARNINGS & CAUTIONS
Installers and operating personnel MUST, at all
times, observe all safety regulations. The
following warnings and cautions are general and
must be given the same attention as specific
precautions included in these instructions. In
addition to all the requirements included in this
AERCO Instruction Manual, the installation of
units MUST conform with local building codes,
or, in the absence of local codes, ANSI Z223.1
(National Fuel Gas Code Publication No. NFPA-
54). Where ASME CSD-1 is required by local
jurisdiction, the installation must conform to
CSD-1.
Where applicable, the equipment shall be
installed in accordance with the current
Installation Code for Gas Burning Appliances
and Equipment, CGA B149, and applicable
Provincial regulations for the class; which should
be carefully followed in all cases. Authorities
having jurisdiction should be consulted before
installations are made.
IMPORTANT
This Instruction Manual is an integral
part of the product and must be
maintained in legible condition. It must
be given to the user by the installer
and kept in a safe place for future
reference.
WARNINGS!
MUST BE OBSERVED TO PREVENT
SERIOUS INJURY.
WARNING!
BEFORE ATTEMPTING TO PER-
FORM ANY MAINTENANCE ON THE
UNIT, SHUT OFF ALL GAS AND
ELECTRICAL INPUTS TO THE UNIT.
WARNING!
THE EXHAUST VENT PIPE OF THE
UNIT OPERATES UNDER A
POSITIVE PRESSURE AND THERE-
FORE MUST BE COMPLETELY
SEALED TO PREVENT LEAKAGE
OF COMBUSTION PRODUCTS INTO
LIVING SPACES.
WARNING
DO NOT USE MATCHES, CANDLES,
FLAMES, OR OTHER SOURCES OF
IGNITION TO CHECK FOR GAS
LEAKS.
WARNING!
FLUIDS UNDER PRESSURE MAY
CAUSE INJURY TO PERSONNEL
OR DAMAGE TO EQUIPMENT
WHEN RELEASED. BE SURE TO
SHUT OFF ALL INCOMING AND
OUTGOING WATER SHUTOFF
VALVES. CAREFULLY DECREASE
ALL TRAPPED PRESSURES TO
ZERO BEFORE PERFORMING
MAINTENANCE.
WARNING!
ELECTRICAL VOLTAGES UP TO
460 VAC MAY BE USED IN THIS
EQUIPMENT. THEREFORE THE
COVER ON THE UNIT’S POWER
BOX (LOCATED BEHIND THE
FRONT PANEL DOOR) MUST BE
INSTALLED AT ALL TIMES, EXCEPT
DURING MAINTENANCE AND
SERVICING.
CAUTIONS!
Must be observed to prevent
equipment damage or loss of
operating effectiveness.
CAUTION!
Many soaps used for gas pipe leak
testing are corrosive to metals. The
piping must be rinsed thoroughly with
clean water after leak checks have
been completed.
CAUTION!
DO NOT use this boiler if any part has
been under water. Call a qualified
service technician to inspect and
replace any part that has been under
water.

SAFETY PRECAUTIONS
1-2
1.2 EMERGENCY SHUTDOWN
If overheating occurs or the gas supply fails to
shut off, close the manual gas shutoff valve
(Figure 1-1) located external to the unit.
IMPORTANT
The Installer must identify and indicate
the location of the emergency shutdown
manual gas valve to operating personnel.
Figure 1-1
Manual Gas Shutoff Valve
1.3 PROLONGED SHUTDOWN
After prolonged shutdown, it is recommended
that the startup procedures in Chapter 4 and the
safety device test procedures in Chapter 6 of
this manual be performed, to verify all system-
operating parameters. If there is an emergency,
turn off the electrical power supply to the
AERCO boiler and close the manual gas valve
located upstream the unit. The installer is to
identify the emergency shut-off device.

INSTALLATION
2-1
CHAPTER 2 INSTALLATION
2.1 INTRODUCTION
This Chapter provides the descriptions and
procedures necessary to unpack, inspect and
install the AERCO Benchmark 3.0 Boiler. Brief
descriptions are also provided for each available
mode of operation. Detailed procedures for
implementing these modes are provided in
Chapter 5.
2.2 RECEIVING THE UNIT
Each Benchmark 3.0 System is shipped as a
single crated unit. The shipping weight is
approximately 2,170 pounds. The unit must be
moved with the proper rigging equipment for
safety and to avoid equipment damage. The unit
should be completely inspected for evidence of
shipping damage and shipment completeness at
the time of receipt from the carrier and before
the bill of lading is signed.
NOTE
AERCO is not responsible for lost or
damaged freight.
Each unit has a Tip-N-Tell indicator on the
outside of the crate. This indicates if the unit has
been turned on its side during shipment. If the
Tip-N-Tell indicator is tripped, do not sign for the
shipment. Note the information on the carrier’s
paperwork and request a freight claim and
inspection by a claims adjuster before
proceeding. Any other visual damage to the
packaging materials should also be made clear
to the delivering carrier.
2.3 UNPACKING
Carefully unpack the unit taking care not to
damage the unit enclosure when cutting away
packaging materials
A close inspection of the unit should be made to
ensure that there is no evidence of damage not
indicated by the Tip-N-Tell indicator. The freight
carrier should be notified immediately if any
damage is detected.
The following accessories come standard with
each unit and are either packed separately
within the unit’s packing container or are factory
installed on the boiler:
•Pressure/Temperature Gauge
•Spare Spark Igniter
•Spare Flame Detector
•ASME Pressure Relief Valve
•Condensate Drain Trap
•2” Gas Supply Shutoff Valve
When ordered, optional accessories may be
packed separately, packed within the boiler
shipping container, or may be installed on the
boiler. Any standard or optional accessories
shipped loose should be identified and stored in
a safe place until ready for installation or use.
2.4 SITE PREPARATION.
Ensure that the site selected for installation of
the Benchmark 3.0 Boiler includes:
•Access to AC Input Power corresponding to
the ordered power configuration. The
available power configurations are:
•208 VAC, 3-Phase, 60 Hz @ 20 A
•460 VAC, 3-Phase, 60 Hz @ 15 A
•Access to Natural Gas line at a static
pressure between 4 and 10 inches W.C.
2.4.1 Installation Clearances
The unit must be installed with the prescribed
clearances for service as shown in Figure 2-1.
The minimum clearance dimensions, required by
AERCO, are listed below. However, if Local
Building Codes require additional clearances,
these codes shall supersede AERCO’s
requirements. Minimum acceptable clearances
required are:
•Sides: 24 inches
•Front : 24 inches
•Rear: 43 inches
•Top: 18 inches
All gas piping, water piping and electrical conduit
or cable must be arranged so that they do not
interfere with the removal of any panels, or
inhibit service or maintenance of the unit.

INSTALLATION
2-2
Figure 2-1 Benchmark 3.0 Boiler Clearances
WARNING
KEEP THE UNIT AREA CLEAR AND
FREE FROM ALL COMBUSTIBLE
MATERIALS AND FLAMMABLE
VAPORS OR LIQUIDS.
CAUTION
While packaged in the shipping
container, the boiler must be moved
by pallet jack or forklift from the
FRONT ONLY.
2.4.2 Setting the Unit
The unit must be installed on a 4 inch to 6 inch
housekeeping pad to ensure proper condensate
drainage. If anchoring the unit, refer to the
dimensional drawings in Appendix F for anchor
locations. A total of 3 lifting tabs are provided at
the top of the primary heat exchanger as shown
in Figure 2-2. However, USE ONLY TABS 1
AND 2 SHOWN IN FIGURE 2-2 TO MOVE THE
ENTIRE UNIT. Tabs 1 and 3 are used only
when removing or replacing the unit’s primary
heat exchanger. Remove the front top panel
from the unit to provide access to the lifting tabs.
Remove the four (4) lag screws securing the unit
to the shipping skid. Lift the unit off the shipping
skid and position it on the 4 inch to 6 inch
housekeeping concrete pad (required) in the
desired location.
Figure 2-2
Lifting Lug Locations
In multiple unit installations, it is important to
plan the position of each unit in advance.
Sufficient space for piping connections and
future service/maintenance requirements must
also be taken into consideration. All piping must
include ample provisions for expansion.
If installing a Combination Control Panel (CCP)
system, it is important to identify the
Combination Mode Boilers in advance and place
them in the proper physical location. Refer to
Chapter 5 for information on Combination Mode
Boilers.

INSTALLATION
2-3
2.4.3 Removal of Support Rod
Prior to installation of water supply and return
piping, the 24” threaded rod shown in Figure 2-3
must be removed. This rod is installed prior to
shipment from the factory to prevent damage to
the insulated metal flex hose on the hot water
supply outlet of the boiler. In order to install the
water supply piping, this rod must be removed
as follows:
1. Refer to Figure 2-3 and back off the hex nut
on the outlet side of the flex hose.
2. Next, disconnect the coupling nut from the
flange stud.
3. Completely remove the threaded rod, hex
nut and coupling nut from the boiler.
5/8-11 x 24" LONG
THREADED ROD 5/8-11
HEX NUT
5
/
8-11
COUPLING NUT
EXHAUST
MANIFOLD
OUTLET
FLANGE
(SEE IMPORTANT
NOTE BELOW)
PARTIAL TOP VIEW - REAR
Figure 2-3
Location of Threaded Support Rod
IMPORTANT
THE INSULATED FLEX HOSE
SHOWN IN FIGURE 2-3 MUST BE
LEVEL OR SLOPING UPWARD AS
IT EXITS THE BOILER. FAILURE TO
PROPERLY POSITION THIS HOSE
MAY CAUSE INEFFECTIVE AIR
ELIMINATION RESULTING IN ELE-
VATED TEMPERATURES THAT
COULD COMPROMISE THE TOP
HEAD GASKET.
2.5 SUPPLY AND RETURN PIPING
The Benchmark 3.0 Boiler utilizes 4” 150#
flanges for the water system supply and return
piping connections. The physical location of the
supply and return piping connections are on the
rear of the unit as shown in Figure 2-4. Refer to
Appendix F, Drawing AP-A-811 for additional
dimensional data.
Figure 2-4
Supply and Return Locations
2.6 CONDENSATE DRAINS
The Benchmark 3.0 Boiler is designed to
condense water vapor from the flue products.
Therefore, the installation must have provisions
for suitable condensate drainage or collection.
Two condensate drain connections are provided
on the rear of the unit as shown in Figure 2-5.
One drain connection is located on the exhaust
manifold and the other is located on the
connecting manifold.
The drain at the bottom of the exhaust manifold
also includes a condensate trap containing a
float assembly. When condensate collects in the
exhaust manifold, the float rises, thereby
allowing it to discharge through the drain
opening. The drain pipe located on the
connecting manifold must be connected to a
second condensate trap which is packed
separately within the unit’s shipping container.
The procedures to install and connect both of
the condensate drains are provided in
paragraphs 2.6.1 and 2.6.2.

INSTALLATION
2-4
SHELL DRAIN
VALVE
EXHAUST
MANIFOLD
REAR VIEW
A
A
B
B
CONDENSATE
TRAP
DRAIN
CONNECTING
MANIFOLD
DRAIN
UNIT
FRAME
CONNECTING
MANIFOLD
DRAIN
VALVE
CONDENSATE
DRAIN PIPE
TO
CONDENSATE
TRAP
SHELL
VIEW “B - B”
VIEW “A - A”
UNIT
FRAME
EXHAUST
MANIFOLD
CONDENSATE
TRAP
DRAIN
HOSE
CLAMP
1" I.D.
HOSE
TO FLOOR
DRAIN
Figure 2-5
Condensate Drain Connection Location
2.6.1 Exhaust Manifold Condensate
Drain
Refer to Figure 2-5, View A – A and install as
follows:
1. Connect a length of 1 inch I.D. hose (part no.
91030) to the drain on the connecting manifold
and secure it in place with a hose clamp.
2. Route the hose to a nearby floor drain.
2.6.2 Connecting Manifold Condensate
Drain
The connecting manifold drain pipe shown in
Figure 2-5, View B – B must be connected to a
separate condensate drain trap external to the
unit. Refer to Figure 2-6 and install the trap as
follows:
NOTE
The condensate trap described in the
following steps can be installed on the
floor behind the unit as shown in Figure 2-
6. There will be sufficient downward slope
from the drain pipe to the trap inlet to
drain the condensate by gravity. Ensure
that the outlet hose from the trap slopes
away (down) from the trap.
1. Position the supplied condensate trap (part
no. 24060) on the floor at the rear of the
unit.
2. Install 3/4” NPT nipples in the tapped inlet
and outlet of the condensate trap.
3. Attach a length of 1½” I.D (part no. GM-
123352). hose between the connecting
manifold drain pipe and the inlet side of the
condensate trap (Figure 2-6). Secure both
ends of the hose with clamps.
4. Connect a second length of 1” I.D.
polypropylene hose to the outlet side of the
condensate trap and route it to a nearby floor
drain.
If desired, a Tee fitting may be used to connect the
two drain hoses from the exhaust manifold and the
outlet side of the of the condensate trap connected
in
If a floor drain is not available, a condensate pump
can be used to remove the condensate to drain.
The maximum condensate flow rate is 20 GPH.
The condensate drain trap, associated fittings and
drain lines must be removable for routine
maintenance. Therefore, DO NOT hard pipe.
Figure 2-6
Condensate Trap Installation

INSTALLATION
2-5
2.7 GAS SUPPLY PIPING
The AERCO Benchmark 3.0 Gas Components
and Supply Design Guide, GF-3030 must be
consulted prior to designing or installing any gas
supply piping.
WARNING
NEVER USE MATCHES, CANDLES,
FLAMES OR OTHER SOURCES OF
IGNITION TO CHECK FOR GAS
LEAKS.
CAUTION
Many soaps used for gas pipe leak
testing are corrosive to metals. There-
fore, piping must be rinsed thoroughly
with clean water after leak checks
have been completed.
NOTE
All gas piping must be arranged so that it
does not interfere with removal of any
covers, inhibit service/maintenance, or
restrict access between the unit and
walls, or another unit.
A 2 inch gas inlet connection is located on the
rear of the unit as shown in Figure 2-4.
Prior to installation, all pipes should be de-
burred and internally cleared of any scale, metal
chips or other foreign particles. Do Not install
any flexible connectors or unapproved gas
fittings. Piping must be supported from the floor,
ceiling or walls only and must not be supported
by the unit.
A suitable piping compound, approved for use
with natural gas, should be used. Any excess
must be wiped off to prevent clogging of
components.
To avoid unit damage when pressure testing gas
piping, isolate the unit from the gas supply
piping. At no time should the gas pressure
applied to the unit exceed 2 psi. Leak test all
external piping thoroughly using a soap and
water solution or suitable equivalent. The gas
piping used must meet all applicable codes.
2.7.1 Gas Supply Specification
The gas supply input specifications to the unit
for Natural Gas are as follows:
The maximum static pressure to the unit must
not exceed 2 psi. The minimum operating gas
pressure for natural gas is 4 inches W.C. for
both FM and IRI gas trains when the unit is firing
at maximum input. The gas supply pressure to
the unit must be of sufficient capacity to provide
3000 cfh while maintaining the gas pressure at 4
inches W.C. for FM or IRI gas trains.
2.7.2 Manual Gas Shutoff Valve
A manual shut-off valve must be installed in the
gas supply line upstream of the Boiler as shown
in Figure 2-7. Maximum allowable gas pressure
to the Boiler is 2 psi
Figure 2-7
Manual Gas Shut-Off Valve Location

INSTALLATION
2-6
2.7.3 IRI Gas Train Kit
The IRI gas train is an optional gas train
configuration which is required in some areas for
code compliance or for insurance purposes.
The IRI gas train is factory pre-piped and wired.
See Appendix F, Drawing AP-A-803 for details.
2.8 AC ELECTRICAL POWER WIRING
The AERCO Benchmark 3.0 Electrical Power
Wiring Guide, GF-3060, must be consulted prior
to connecting any AC power wiring to the unit.
External AC power connections are made to the
unit inside the Power Box on the front panel of
the unit. Remove the front door of the unit to
access the Power Box mounted directly above
the Control Box. Loosen the four Power Box
cover screws and remove cover to access the
AC terminal connections inside the Power Box
(Figure 2-8).
NOTE
All electrical conduit and hardware must
be installed so that it does not interfere
with the removal of any unit covers, inhibit
service/maintenance, or prevent access
between the unit and walls or another
unit.
Figure 2-8
AC Input Terminal Block Location
2.8.1 Electrical Power Requirements
The AERCO Benchmark 3.0 Boiler is available
in two different AC power configurations:
•208 VAC/3-Phase/60 @20 amps
•460 VAC/3-Phase/60 Hz @ 15 amps
Each of the power configurations utilize a Power
Box with a terminal block that matches the
configuration ordered. The two different terminal
block configurations are shown in Figure 2-9. A
wiring diagram showing the required AC power
connections is provided on the front cover of the
Power Box.
Each Benchmark 3.0 Boiler must be connected
to a dedicated electrical circuit. NO OTHER
DEVICES SHOULD BE ON THE SAME
ELECTRICAL CIRCUIT AS THE BENCHMARK
BOILER. A means for disconnecting AC power
from the unit (such as a service switch) must be
installed near the unit for normal operation and
maintenance. All electrical connections should
be made in accordance with the National
Electrical Code and/or with any applicable local
codes.
For electrical power wiring diagrams, see the
AERCO Benchmark 3.0 Electrical Power Wiring
Guide, (GF-3060).
Figure 2-9
AC Terminal Block Configurations

INSTALLATION
2-7
2.9 MODES OF OPERATION AND FIELD
CONTROL WIRING
The Benchmark 3.0 Boiler is available in several
different modes of operation. While each unit is
factory configured and wired for its intended
mode, some additional field wiring may be
required to complete the installation. This wiring
is typically connected to the Input/Output (I/O)
Box located on the lower portion of the unit front
panel (Figure 2-10) behind the removable front
door.
To access the I/O Box terminal strips shown in
Figure 2-10, loosen the four cover screws and
remove the cover. All field wiring is installed
from the rear of the panel by routing the wires
through one of the four bushings provided.
Refer to the wiring diagram provided on the
cover of the I/O Box (Figure 2-11) when making
all wiring connections.
In addition to the terminal strips shown in Figure
2-10, the I/O Box also contains a pre-wired
temperature transmitter which receives inlet air
temperature sensor readings and transmits this
signal to the variable frequency drive (VFD)
contained in the Benchmark 3.0 Boiler. The VFD
utilizes this input signal to adjust the rotation
speed of the blower.
Figure 2-10.
Input/Output (I/O) Box Location
Brief descriptions of each mode of operation,
and their wiring requirements, are provided in
the following paragraphs. Additional information
concerning field wiring is provided in paragraphs
2.9.1 through 2.9.9. Refer to Chapter 5 for
detailed information on the available modes of
operation.
Figure 2-11. I/O Box Terminal Strip

INSTALLATION
2-8
2.9.1 Constant Setpoint Mode
The Constant Setpoint Mode is used when it is
desired to have a fixed setpoint that does not
deviate. No wiring connections, other than AC
electrical power connections, are required for
this mode. However, if desired, fault monitoring
or enable/disable interlock wiring can be utilized
(see paragraphs 2.9.9.1 and 2.9.10).
2.9.2 Indoor/Outdoor Reset Mode
This mode of operation increases supply water
temperature as outdoor temperatures decrease.
An outside air temperature sensor (AERCO Part
No. 122790) is required. The sensor MUST BE
wired to the I/O Box wiring terminals (see Figure
2-11). Refer to paragraph 2.10.1 for additional
information on outside air temperature sensor
installation.
2.9.3 Boiler Management System Mode
NOTE
BMS Model 168 can utilize either pulse
width modulation (PWM) or RS485
Modbus signaling to the Boiler. BMS II
Model 5R5-384 can utilize only RS485
signaling to the Boiler.
When using an AERCO Boiler Management
System (BMS), the field wiring is connected
between the BMS Panel and each Boiler’s I/O
Box terminal strip (Figure 2-11). Twisted
shielded pair wire from 18 to 22 AWG must be
utilized for the connections. The BMS Mode can
utilize either pulse width modulation (PWM)
signaling, or RS485 Modbus signaling. For PWM
signaling, connections are made from the
AERCO Boiler Management System to the
B.M.S. (PWM) IN terminals on the I/O Box
terminal strip. For RS485 Modus signaling,
connections are made from the BMS to the
RS485 COMM terminals on the I/O Box terminal
strip. Polarity must be maintained and the shield
must be connected only at the AERCO BMS.
The boiler end of the shield must be left floating.
For additional instructions, refer to Chapter 5,
paragraph 5.6 in this manual. Also, refer to GF-
108M (BMS Model 168) and GF-124 (BMS II
Model 5R5-384), BMS -Operations Guides.
2.9.4 Remote Setpoint and Direct Drive
Modes
The Benchmark 3.0 Boiler can accept several
types of signal formats from an Energy
Management System (EMS), Building
Automation System (BAS) or other source, to
control either the setpoint (Remote Setpoint
Mode) or firing rate (Direct Drive Mode) of the
Boiler. These formats are:
•4 to 20 mA/1 to 5 VDC
•0 to 20 mA/0 to 5 VDC
•PWM – (Pulse Width Modulated signal. See
para. 2.10.4)
•Network (RS485 Modbus. See para. 2.10.7)
While it is possible to control a boiler or boilers
using one of the previously described modes of
operation, it may not be the method best suited
for the application. Prior to selecting one of
these modes of operation, it is recommended
that you consult with your local AERCO
representative or the factory for the mode of
operation that will work best with your
application. For more information on wiring the
4 to 20 mA / 1to 5VDC or the 0 to 20 mA / 0 to 5
VDC, see paragraph 2.9.3.
2.9.5 Combination Mode
NOTE
Only BMS Model 168 can be utilized for
the Combination Mode, not the BMS II
(Model 5R5-384).
With a Combination Mode unit, field wiring is
between the unit’s I/O Box wiring terminals, the
CCP (Combination Control Panel), and the BMS
Model 168 (Boiler Management System). The
wiring must be accomplished using twisted-
shielded pair wire from 18 to 22 AWG. Polarity
must be maintained. For further instructions and
wiring diagrams, refer to the GF-108 Boiler
Management System Operations Guide and the
CCP-1 data sheet.
2.10 I/O BOX CONNECTIONS
The types of input and output signals and
devices to be connected to the I/O Box terminals
shown in Figure 2-11 are described in the
following paragraphs.
CAUTION
DO NOT make any connections to the
I/O Box terminals labeled “NOT
USED”. Attempting to do so may
cause equipment damage.
2.10.1 OUTDOOR SENSOR IN
An outdoor air temperature sensor (AERCO Part
No. 122790) will be required primarily for the
Indoor/Outdoor reset mode of operation. It can
also be used with another mode if it is desired to
use the outdoor sensor enable/disable feature.
This feature allows the boiler to be enabled or
disabled based on the outdoor air temperature.

INSTALLATION
2-9
The factory default for the outdoor sensor is
DISABLED. To enable the sensor and/or select
an enable/disable outdoor temperature, see the
Configuration menu in Chapter 3.
The outdoor sensor may be wired up to 200 feet
from the boiler. It is connected to the
OUTDOOR SENSOR IN and SENSOR
COMMON terminals in the I/O Box (see Figures
2-10 and 2-11). Wire the sensor using a twisted
shielded pair wire from 18 to 22 AWG. There is
no polarity to observe when terminating these
wires. The shield is to be connected only to the
terminals labeled SHIELD in the I/O Box. The
sensor end of the shield must be left free and
ungrounded.
When mounting the sensor, it must be located
on the North side of the building where an
average outside air temperature is expected.
The sensor must be shielded from direct sunlight
as well as impingement by the elements. If a
shield is used, it must allow for free air
circulation.
2.10.2 AUX SENSOR IN
The AUX SENSOR IN terminals can be used to
add an additional temperature sensor for
monitoring purposes. This input is always
enabled and is a view-only input that can be
seen in the Operating Menu. The sensor must
be wired to the AUX SENSOR IN and SENSOR
COMMON terminals and must be similar to
AERCO BALCO wire sensor Part No. 12449. A
resistance chart for this sensor is provided in
Appendix C.
2.10.3 ANALOG IN
The ANALOG IN + and – terminals are used
when an external signal is used to drive the
firing rate (Direct Drive Mode) or change the
setpoint (Remote Setpoint Mode) of the Boiler.
Either a 4 to 20 mA /1 to 5 VDC or a 0 to 20 mA
/ 0 to 5 VDC signal may be used to vary the
setpoint or firing rate. The factory default setting
is for 4 to 20 mA / 1 to 5 VDC, however this may
be changed to 0 to 20 mA / 0 to 5 VDC using the
Configuration Menu described in Chapter 3. If
voltage rather than current is selected as the
drive signal, a DIP switch must be set on the
PMC Board located inside the Control Box.
Contact the AERCO factory for information on
setting DIP switches.
All of the supplied signals must be floating
(ungrounded) signals. Connections between the
signal source and the Boiler’s I/O Box must be
made using twisted shielded pair wire from 18 to
22 AWG, such as Belden 9841 (see Figure
2-11). Polarity must be maintained. The shield
must be connected only at the source end and
must be left floating (not connected) at the
Boiler’s I/O Box.
Regardless of whether voltage or current is used
for the drive signal, they are linearly mapped to
a 40°F to 240°F setpoint or a 0% to 100% firing
rate. No scaling for these signals is provided
2.10.4 B.M.S. (PWM) IN
NOTE
Only BMS Model 168 can utilize Pulse
Width Modulation (PWM), not the BMS II
(Model 5R5-384).
These terminals are used to connect the
AERCO Boiler Management System (BMS)
Model 168 to the unit. The BMS Model 168
utilizes a 12 millisecond, ON/OFF duty cycle.
This duty cycle is Pulse Width Modulated (PWM)
to control firing rate. A 0% firing rate = a 5% ON
pulse and a 100% firing rate = a 95% ON pulse.
2.10.5 SHIELD
The SHIELD terminals are used to terminate any
shields used on sensor wires connected to the
unit. Only shields must be connected to these
terminals.
2.10.6 mA OUT
These terminals provide a 4 to 20 mA output to
the VFD to control the rotational speed of the
blower. This function is enabled in the
Configuration Menu (Chapter 3, Table 3.4).
2.10.7 RS-485 COMM
These terminals are used for RS-485 MODBUS
serial communication between the unit and an
external “Master” such as a Boiler Management
System (BMS), Energy Management System
(EMS), Building Automation System (BAS) or
other suitable device.
2.10.8 EXHAUST SWITCH IN
These terminals permit an external exhaust
switch to be connected to the exhaust manifold
of the boiler. The exhaust switch should be a
normally open type switch (such as AERCO Part
No. 123463) that closes (trips) at 500°F.
2.10.9 INTERLOCKS
The unit offers two interlock circuits for
interfacing with Energy Management Systems
and auxiliary equipment such as pumps or
louvers. These interlocks are called the Remote
Interlock and Delayed Interlock (Figure 2-11).
The wiring terminals for these interlocks are

INSTALLATION
2-10
located inside the I/O Box on the unit front
panel. The I/O Box cover contains a wiring
diagram which shows the terminal strip locations
for these interlocks (REMOTE INTL’K IN and
DELAYED INTL’K IN). Both interlocks,
described below, are factory wired in the closed
position.
NOTE
Both the Delayed Interlock and Remote
Interlock MUST be in the closed position
to allow the unit to fire.
2.10.9.1 REMOTE INTERLOCK IN
The remote interlock circuit is provided to
remotely start (enable) and stop (disable) the
Boiler, if desired. The circuit is labeled
REMOTE INTL’K IN and is located inside the I/O
Box on the front panel. The circuit is 24 VAC
and is factory pre-wired in the closed (jumpered)
position.
2.10.9.2 DELAYED INTERLOCK IN
The delayed interlock is typically used in
conjunction with the auxiliary relay described in
paragraph 2.10. This interlock circuit is located
in the purge section of the start string. It can be
connected to the proving device (end switch,
flow switch etc.) of an auxiliary piece of
equipment started by the Boiler’s auxiliary relay.
The delayed interlock must be closed for the
boiler to fire.
If the delayed interlock is connected to a proving
device that requires time to close (make), a time
delay (Aux Start On Dly) that holds the start
sequence of the boiler long enough for a proving
switch to make can be programmed. Should the
proving switch not prove within the programmed
time frame, the boiler will shut down. The Aux
Start On Dly can be programmed from 0 to 120
seconds. This option is locate in the
Configuration Menu (Chapter 3, Table 3-4).
2.10.10 FAULT RELAY
The fault relay is a single pole double throw
(SPDT) relay having a normally open and
normally closed set of relay contacts that are
rated for 5 amps at 120 VAC and 5 amps at 30
VDC. The relay energizes when any fault
condition occurs and remains energized until the
fault is cleared and the CLEAR button is
depressed. The fault relay connections are
shown in Figure 2-11.
2.11 AUXILIARY RELAY CONTACTS
Each Boiler is equipped with a single pole
double throw (SPDT) relay that is energized
when there is a demand for heat and de-
energized after the demand for heat is satisfied.
The relay is provided for the control of auxiliary
equipment, such as pumps and louvers, or can
be used as a Boiler status indictor (firing or not
firing). Its contacts are rated for 120 VAC @ 5
amps. Refer to Figure 2-11 to locate the AUX
RELAY terminals for wiring connections.
2.12 FLUE GAS VENT INSTALLATION
The minimum allowable vent diameter for a
single Benchmark 3.0 Boiler is 8 inches.
The AERCO Benchmark Venting and
Combustion Air Guide, GF-3050, must be
consulted before any flue gas vent or inlet air
venting is designed or installed. U/L listed,
positive pressure, watertight vent materials as
specified in AERCO’s GF-3050, must be used
for safety and code compliance. Since the unit is
capable of discharging low temperature exhaust
gases, horizontal sections of the flue vent
system must be pitched back to the unit a
minimum of 1/4 inch per foot to avoid
condensate pooling and allow for proper
drainage.
The combined pressure drop of vent and
combustion air systems must not exceed 140
equivalent feet of 8 inch ducting. Fittings as well
as pipe lengths must be calculated as part of the
equivalent length.
For a natural draft installation the draft must not
exceed ±0.25 inch W.C. These factors must be
planned into the vent installation. If the
maximum allowable equivalent lengths of piping
are exceeded, the unit will not operate properly
or reliably.
2.13 COMBUSTION AIR
The AERCO Benchmark Venting and
Combustion Air Guide, GF-3050 MUST be
consulted before any flue or combustion supply
air venting is designed or implemented.
Combustion air supply is a direct requirement of
ANSI 223.1, NFPA-54, and local codes. These
codes should be consulted before a permanent
design is determined.