Crest Audio Sync Condensing Boiler 1.5 User manual

FB-MODB Rev A
This manual must only be used
by a qualified heating installer /
service technician. Read all
instructions, including this manual,
the Installation and Operation
Manual, and the Service Manual,
before installing. Perform steps in
the order given. Failure to comply
could result in severe personal
injury, death, or substantial property
damage.
WARNING
Save this manual for future reference.
MODBUS COMMUNICATION
INSTRUCTIONS
Crest Models: 1.5 - 3.5

2
1 Introduction
The information contained in this manual provides general guidelines for the implementation of ModBus communication with
the Lochinvar Crest boiler.
All ModBus networks are implemented utilizing a master-slave arrangement where all Crest boilers are slaves and the master is
a building automation system capable of communicating over a RS-485 serial connection.
Contents
1. INTRODUCTION
Definitions.................................................................... 2
Minimum System Requirements.................................. 2
2. CONFIGURATION
Addressing................................................................... 3
Timing Specifications................................................... 4
Parity............................................................................ 4
Data Transmission Mode............................................. 4
ModBus Board Diagnostics......................................... 4
Internal Faults......................................................... 4
ModBus Function Set............................................. 5
ModBus Exception Codes........................................... 6
3. MEMORY MAP
Primary Data Tables..................................................... 7
Crest Boiler Memory Map............................................7-8
Input Registers........................................................ 8
Holding Registers.................................................... 8
Configuration Bits......................................................... 8
4. WIRING REQUIREMENTS
Physical Wiring............................................................. 9
Typical Boiler System Wiring..................................12-13
5. UNIT OPERATION
Unit Operation with ModBus Communications...... 14-17
6. TROUBLESHOOTING........................................... 18-21
7. DIAGRAMS
Ladder Diagram............................................................22
Wiring Diagram............................................................ 23
Revision Notes................................................... Back Cover
Abbreviation or Acronym Meaning
ASCII American Standard Code for Information Interchange
BAS Building Automation System
Baud (Baud Rate) Number of data bits transmitted per second (bps)
EMS Energy Management System
FDX Full-Duplex
HDX Half-Duplex
Hex Hexadecimal Number (0 - 9, A - F)
I/O Box Input/Output (I/O)
LSB Least Significant Byte
ModBus® A serial, half-duplex data transmission protocol developed by AEG Modicon
MSB Most Significant Byte
RS232 A standard for serial, full-duplex (FDX) transmission of data based on the
RS232 Standard
RS485 A standard for serial transmission of data based on the RS-485 Standard
RTU Remote Terminal Unit
Definitions
Minimum System Requirements
• BAS system or computer with a serial or USB port with a converter to RS-485.
Shielded twisted pair communication cable.

3
2 Configuration
Addressing
The ModBus addressing space is comprised of 256 different
addresss.
• 0 is reserved for broadcast messages from the master
device
• 1 - 247 are free to use for each unique device
• 248 - 255 are reserved
To set the ModBus address the dip switches can be set in
either the 0 position or the 1 position. For switches set to
the 1 position their value will be added together to determine
the address.
For each switch set to the 1 position it has the following value:
Dip switch 1 = 1
Dip switch 2 = 2
Dip switch 3 = 4
Dip switch 4 = 8
Dip switch 5 = 16
Dip switch 6 = 32
Dip switch 7 = 64
Dip switch 8 = 128
Any dip switch set to 0 has a value equal to 0.
Example:
To set the address of the ModBus board to 50, dip switches
2, 5, and 6 have to be set to the 1 position. The address is
determined by adding the values of all the dip switches together.
Address = Value of Dip switch 1 + Value of Dip switch 2 +
Value of Dip switch 3 + Value of Dip switch 4 + Value of Dip
switch 5 + Value of Dip switch 6 + Value of Dip switch 7 +
Value of Dip switch 8
In this example:
Address = 0 + 2 + 0 + 0 + 16 + 32 + 0 + 0 = 50
The ModBus communication board is equipped with a set of ten dip switches that are used to set the board configuration
(address, baud rate, and parity settings). The first eight are used to set the address of each board. The ninth is used to set the
baud rate. The tenth is used to set the parity.
LED’S
DIP SWITCHES
Figure 2-1_ModBus Communication Board
ModBus Instructions

4
2 Configuration
Timing Specifications
The baud rate for the ModBus board is selectable with Dip
switch #9.
1 = 19200 bps
0 = 9600 bps
Each message is started by at least 3.5 character times of
silence. The maximum delay between frames is 1.5 character
times.
When the system temperature and/or tank temperature
is provided by the BAS to the boiler, it is critical that
the temperature be updated every few seconds. If the
boiler does not receive updated temperatures within a
timeout period (installer adjustable), the control will revert
to using its own sensor inputs (if sensors are connected).
The timeout is programmable by pressing the MAIN
MENU>>SETUP>>MODBUS buttons. The timeout is
adjustable between 5 and 120 seconds. The default timeout
is 10 seconds.
When the BAS is not providing either of these temperatures,
but is still controlling the boiler (such as providing a
modulation command), the BAS must refresh these
commands at least every 4 minutes. If the commands are
not refreshed, the boiler will revert to operating based on its
own inputs.
Parity
Parity is set by the position of Dip switch #10.
0 = No Parity
1 = Even Parity
If No Parity is selected there will be two stop bits, otherwise
there will be one.
Data Transmission Mode
Many ModBus bus master devices can be configured to
transmit data in either ModBus RTU or ModBus ASCII modes.
Since RTU messages can be formatted to use fewer data bits and
are therefore more efficient, RTU has been chosen to be used
with all Lochinvar ModBus communication. Please ensure that
the master device is transmitting ModBus RTU.
ModBus Board Diagnostics
The ModBus board is equipped with three LED’s for visual
diagnostics: Two yellow LED’s and one green. One yellow LED
(D5) is used to indicate reception of data. The other yellow
LED (D6) is used to indicate transmission of data. The green
LED (D7) is used to show internal faults.
Internal Faults:
Normal Operation = 1 second bright, 1 second dim
Controller Fault = Continuously on
No Burner Control Communication = 0.5 seconds on, 1.5
seconds off
No ModBus Communication = 1.5 seconds on, 0.5 seconds
off
ModBus Communication
The ModBus communication commands and exception codes
that are supported by the ModBus communication board can
be found on pages 5 and 6 of this manual.
ModBus Instructions

5
2 Configuration (continued)
Function Sub Function HEX Description
Dec HEX Dec
1 01 Read Coil Status
2 02 Read Input Status
3 03 Read Holding Registers
4 04 Read Input Registers
5 05 Force Single Coil
6 06 Preset Single Register
7 07 Read Exception Status
8 08 0 00 Diagnostic - Return Query Data
1 01 Diagnostic - Restart Communication
2 02 Diagnostic - Return Diagnostic Register
4 04 Diagnostic - Force Listen Mode
10 0A Diagnostic - Clear Counters and Diagnostic
Registers
11 0B Diagnostic - Return Bus Message Count
12 0C Diagnostic - Bus Communication Error Count
13 0D Diagnostic - Bus Exception Error Count
14 0E Diagnostic - Return Slave Message Count
15 0F Diagnostic - Return Communication Error Count
16 10 Diagnostic - Return Slave NAK Count
17 11 Diagnostic - Return Slave Busy Count
18 12 Diagnostic - Return Bus Character Overrun Count
20 14 Diagnostic - Clear Overrun Counter and Flag
11 0B Get Communication Event Counter
12 0C Get Communication Event Log
15 0F Write Multiple Coils
16 10 Write Multiple Registers
17 11 Report Slave ID
23 17 Read / Write Multiple Registers
ModBus Function Set
ModBus Instructions

6
2 Configuration
MODBUS Exception Codes
Code Name Meaning
01 ILLEGAL FUNCTION
The function code received in the query is not an allowable action for the server
(or slave). This may be because the function code is only applicable to newer
devices, and was not implemented in the unit selected. It could also indicate that
the server (or slave) is in the wrong state to process a request of this type, for
example because it is unconfigured and is being asked to return register values.
02 ILLEGAL DATA ADDRESS
The data address received in the query is not an allowable address for the
server (or slave). More specifically, the combination of reference number and
transfer length is invalid. For a controller with 100 registers, the PDU addresses
the first register as 0, and the last one as 99. If a request is submittted with a
starting register address of 96 and a quantity of registers of 4, then this request
will successfully operate (address-wise at least) on registers 96, 97, 98, 99. If
a request is submitted with a starting register address of 96 and a quantity of
registers of 5, then this request will fail with Exception Code 0x02 “Illegal Data
Address” since it attempts to operate on registers 96, 97, 98, 99 and 100, and
there is no register with address 100.
03 ILLEGAL DATA VALUE
A value contained in the query data field is not an allowable value for server
(or slave). This indicates a fault in the structure of the remainder of a complex
request, such as that the implied length is incorrect. It specifically does NOT
mean that a data item submitted for storage in a register has a value outside the
expectation of the application program, since the MODBUS protocol is unaware of
the significance of any particular value of any particular register.
04 SLAVE DEVICE FAILURE An unrecoverable error occurred while the server (or slave) was attempting to
perform the requested action.
05 ACKNOWLEDGE
Specialized use in conjunction with programming commands. The server (or
slave) has accepted the request and is processing it, but a long duration of time
will be required to do so. This response is returned to prevent a timeout error from
occurring in the client (or master). The client (or master) can next issue a Poll
Program Complete message to determine if processing is completed.
06 SLAVE DEVICE BUSY Specialized use in conjunction with programming commands. The server (or slave) is engaged in processing a long -- duration program command. The client
(or master) should re-transmit the message later when the server (or slave) is free.
08 MEMORY PARITY ERROR
Specialized use in conjuction with function codes 20 and 21 and reference type
6, to indicate that the extended file area failed to pass a consistency check. The
server (or slave) attempted to read record file, but detected a parity error in the
memory. The client (or master) can retry the request, but service may be required
on the server (or slave) device.
0A GATEWAY PATH UNAVAILABLE
Specialized use in conjunction with gateways, indicates that the gateway was
unable to allocate an internal communication path from the input port to the
output port for processing as the request. Usually means that the gateway is
misconfigured or overloaded.
0B GATEWAY TARGET DEVICE
FAILED TO RESPOND
Specialized use in conjunction with gateways, indicates that no response was
obtained from the target device. Usually means that the device is not present on
the network.
ModBus Exception Codes
ModBus Instructions

7
Primary Data Tables
Table Data Type Read / Write
Discrete Inputs Single Bit Read Only
Coils Single Bit Read / Write
Input Registers 16-Bit Word Read Only
Holding Registers 16 Bit Word Read / Write
Crest Boiler Memory Map
Coils
Address Description Default Unit Min. Max. Resolution
00001 Boiler Enable 0 1=ON / 0=OFF 0 1 1
00005 Tank Thermostat 0 1=ON / 0=OFF 0 1 1
Discrete Inputs
10001 Manual Reset High Limit 0 1=ON / 0=OFF 0 1 1
10002 Flow Switch 0 1=ON / 0=OFF 0 1 1
10003 Gas Pressure Switch 0 1=ON / 0=OFF 0 1 1
10004 Louver Proving Switch 0 1=ON / 0=OFF 0 1 1
10005 Blower Proving Switch 1 0 1=ON / 0=OFF 0 1 1
10006 Blocked Drain Switch 0 1=ON / 0=OFF 0 1 1
10008 Flame 1 0 1=ON / 0=OFF 0 1 1
10009 Enable 0 1=ON / 0=OFF 0 1 1
10010 Tank Thermostat 0 1=ON / 0=OFF 0 1 1
10011 Blocked Flue 0 1=ON / 0=OFF 0 1 1
10013 Blower Proving Switch 2 0 1=ON / 0=OFF 0 1 1
10021 Flue Damper Proving Switch 0 1=ON / 0=OFF 0 1 1
10023 Flame 2 0 1=ON / 0=OFF 0 1 1
10033 Run-time Contacts 0 1=ON / 0=OFF 0 1 1
10034 Alarm Contacts 0 1=ON / 0=OFF 0 1 1
10035 SH Pump 0 1=ON / 0=OFF 0 1 1
10036 DHW Pump 0 1=ON / 0=OFF 0 1 1
10038 Gas Valve 1 0 1=ON / 0=OFF 0 1 1
10039 System Pump 0 1=ON / 0=OFF 0 1 1
10044 Vent Damper Relay 0 1=ON / 0=OFF 0 1 1
10046 Gas Valve 2 0 1=ON / 0=OFF 0 1 1
10049 Blower #1 Power 0 1=ON / 0=OFF 0 1 1
10050 Blower #2 Power 0 1=ON / 0=OFF 0 1 1
10051 Spark Igniter 0 1=ON / 0=OFF 0 1 1
3 Memory Map
ModBus Instructions

8
Input Registers
Address Description Default Unit Min. Max. Resolution
30001 Discrete Inputs 1 - 16 0 NA 0 65535 1
30002 Discrete Inputs 17 - 32 0 NA 0 65535 1
30003 Discrete Inputs 33 - 48 0 NA 0 65535 1
30004 System / Cascade Setpoint 0 Degrees Celsius 0 130 0,5
30005 System Pump Speed 0 % 0 100 1
30006 Cascade Total Power 0 % 100 800 1
30007 Cascade Current Power 0 % 0 800 1
30008 Outlet Setpoint 0 Degrees Celsius 0 130 0,5
30009 Outlet Temperature 0 Degrees Celsius 0 130 0,1
30010 Inlet Temperature 0 Degrees Celsius -20 130 0,1
30011 Flue Temperature 0 Degrees Celsius -20 130 0,1
30012 Firing Rate 0 % 0 100 1
30013 Boiler Pump Speed 0 % 0 100 1
30014 Boiler Status Code 0 NA 0 65535 1
30015 Boiler Blocking Code 0 NA 0 65535 1
30016 Boiler Lockout Code 0 NA 0 65535 1
Holding Registers
40001 Configuration 0 NA 0 65535 1
40002 Coils 0 NA 0 65535 1
40003 0-10Volt Input/ RateCommand /Setpoint
Command 0 % 0 100 1
40004 Tank Setpoint 0 Degrees Celsius 0 87,5 0,5
40005 Tank Temperature 0 Degrees Celsius -20 130 0,1
40006 Outdoor Temperature 0 Degrees Celsius -40 60 0,1
40007 System Supply Temperature 0 Degrees Celsius -20 130 0,1
40008 System Return Temperature 0 Degrees Celsius -20 130 0,1
Crest Boiler Memory Map
3 Memory Map
Configuration Bits
Address 40001 contains configuration bits sent from the BAS to the boiler. These bits tell the boiler to use its own internal inputs,
or inputs from the BAS. When a bit is set to 1, the boiler will ignore the corresponding value contained internally, and expect
the BAS to write that value into the Holding Registers. The configuration bits are as follows:
Bit 4: System Supply Temperature
Bit 5: Outdoor Temperature
Bit 6: Tank Temperature
Bit 7: System Return Temperature
Bit 8 - 15: Not Used (Default = 0)
Bit 0 (LSB): Boiler Enable
Bit 1: Tank Thermostat
Bit 2: Rate Command / 10 - 10V Input / Setpoint Command
Bit 3: Tank Setpoint
ModBus Instructions

9
4 Wiring Requirements
RS-485 Communication Bus
• Maximum Length = 4000 feet
• Cable Specification = 24 AWG / A,B (twisted pair) and GND Shielded, with characteristic Impedance = 120 ohm
• Maximum Load = 32 units (32 nodes)
NOTE: Cable must be terminated with 120 ohm impedance matching resistor on each end.
Note that when the System Supply / System Return Temperature and/or the Tank Temperature are provided by the BAS, they
need to be refreshed every few seconds. This is required in order to prevent unwanted fluctuations in these temperatures. If
these values are not provided every few seconds (timeout is programmable), the boiler will revert to its own internal control. If
neither of these temperatures is provided by the BAS, but any of the other control signals are being provided, the BAS will still
need to refresh these inputs at least every 4 minutes.
Physical Wiring
Figure 4-1_Terminal Strip Connections
1
2
3 4
5
6
7
8
9
10
11
12
13
14
15
16
ALARM
CONTAC TS
RUN TIME CONTAC TS
TANK
THERMOSTAT
ENAB LE LOUVER
PROVING LOUVER
RELA Y
AUX
SWITCH 1
AUX SWITCH 2
40 39
38
37 36
35 34
33
32
31
30 29 28 27
26
25 24
23 22
21 20
19
18 17
CASCADE
SYSTEM PUMP
IN
BMS
IN
OUTDOOR
SENSOR SENSOR SENSOR SENSOR
TANK
SYSTEM SUPPLY
SYSTEM RETURN
BOILER PUMP
OUT
OUT
RATE
MODBUS
SHIELD SHIELD B A -
+ +
-
-
- + +
SHIELD
SHIELD B
A
BUILDING
MANAGEMENT
SYSTEM
TANK
THERMOSTAT
ENABLING
DEVICE
LOUVER
PROVING
SWITCH
LOUVER
RELAY
AUX
SWITCH 1
AUX
SWITCH 2
FROM PREVIOUS BOILER TO NEXT BOILER
A B B
A
SHIELD
SHIELD
0-10V INPUT SYSTEM PUMP OUTDOOR SENSOR
TANK SENSOR SYSTEM SUPPLY SENSOR SYSTEM RETURN SENSOR
0-10V OUTPUT
BOILER PUMP
MODBUS
COMMUNICATION BUS
SHIELD
A
B
B A
SHIELD
ModBus Instructions

10
4 Wiring Requirements
Figure 4-2_Control Inputs
ModBus Instructions
GAS PRESSURE SWITCHES
DHW THERMOSTAT /
SENSOR
ENABLING DEVICE
SYSTEM SENSOR -
SUPPLY
OUTDOOR SENSOR
SEQUENCER / BUILDING
MANAGMENT SYSTEM
LOW VOLTAGE
CONNECTION
BOARD
INLET TEMPERATURE
SENSOR
OUTLET TEMPERATURE /
HI-LIMIT SENSOR
FLUE GAS SENSOR
LOUVER PROVING SWITCH
FLAME SENSOR 1 & 2
LOW WATER CUTOFF
BLOCKED DRAIN SWITCH
DISPLAY PANEL PC INTERFACE
SMART CONTROL
MODULE
AIR PRESSURE SWITCH
SYSTEM SENSOR -
RETURN
AUX SWITCH 1 & 2
0-10 INPUT FROM
SYSTEM PUMP
BLOWER PROVING
SWITCHES
CASCADE
INLET AIR SENSORS
MANUAL RESET
HIGH LIMIT
VENT DAMPER
PROVING SWITCH
MODBUS
BOARD

11
4 Wiring Requirements (continued)
Figure 4-3_Control Outputs
ModBus Instructions
LOW VOLTAGE
CONNECTION
BOARD
SMART CONTROL
MODULE
ALARM BELL
LOUVER RELAY
RUN TIME CONTACTS
SEQUENCER / BUILDING
MANAGMENT SYSTEM
BOILER PUMP
CONTACTOR
SYSTEM PUMP
CONTACTOR
HWG PUMP
CONTACTOR
IGNITOR
BLOWERS
GAS VALVES
BOILER RATE OUTPUT
DISPLAY PANEL
PC INTERFACE
120V
SUPPLY
SYSTEM PUMP BOILER PUMP DHWPU MP
MAX. 1.5 AMPS PER CONNECTION
NL FIELDSUPPLIED CONTACTOR MUST
BEINSTALLED
LINE VOLTAGE
TERMINAL
STRIP
0-10V OUTPUT TO
BOILER PUMP
VENT DAMPER

12
4 Wiring Requirements
Figure 4-4_Control Location
MODBUS
COMMUNICATION
BOARD (MTR01)
CONTROLLER
Typical Boiler System Wiring
Cascade Daisy Chain Connection
Modbus RS485 Communication Bus
Modbus RS485 Port on Gateway or Building System
Physical Configuration: Cascade without Individual Monitoring
ModBus Instructions

13
4 Wiring Requirements (continued)
Modbus RS485 Communication Bus
Modbus RS485 Port on Gateway or Building System
Physical Configuration: Direct Control
Cascade Daisy Chain Connection
Modbus RS485 Communication Bus
Modbus RS485 Port on Gateway or Building System
Physical Configuration: Cascade with individual Monitoring
ModBus Instructions

14
5 Unit Operation
Unit Operation with ModBus Communications
To control a Crest boiler through a Building Management System communicating through ModBus, the Crest Demand
Configuration must be set to one of three options. These configurations allow different control points for a variety of applications.
The configuration can be set by selecting Main Menu>>Setup>>BMS.
Holding Registers Definition Bit Value (HEX) Action
40001 Configuration 00 01 Set Configuration to read 40002
40002 Coils 00 01 Enables unit (00 00 disables unit)
NOTE: To ensure proper operation re-send the configuration bits to holding register 40001 prior to issuing a command.
The Crest boiler is equipped with a ModBus communication timer. This timer is programmable from 0 - 120 seconds. The
timer can be programmed from the ModBus Setup Menu by selecting Main Menu>>Setup>>ModBus. The purpose of the
timer is to ensure proper temperature data is communicated to the boiler in a timely manner. Additionally, it will provide for
fail safe operation should ModBus communication be lost. This timer will cause the unit to revert back to internal unit controls
should the ModBus communication be interrupted longer than the ModBus timer. The timer is reset every time a ModBus write
command is received with updated temperatures or commands. It is the recommendation of Lochinvar that this timer be set to
the shortest value possible.
When controlling a Crest boiler through a Building Automation System (BAS), it is very important to ensure that the correct
configuration bits are sent to holding register 40001, and that the correct data and enable signals are sent to holding registers
40002 - 40007, per the demand configuration.
Demand Configuration: ENABLE = ACTIVE; BMS = INACTIVE
In this configuration the unit is controlled by setting the setpoints locally on the boiler and providing an enable signal through
ModBus communications.
All sensors and limiting devices should be hardwired to the terminal strip on the back of the unit excluding the enable signal.
This signal will be sent to the unit via ModBus.
The holding registers will need to be set as follows:
ModBus Instructions

15
5 Unit Operation (continued)
Demand Configuration: ENABLE = INACTIVE; BMS = ACTIVE
In this configuration the unit is controlled by setting the modulation setpoint from 0 - 100%, or the setpoint. The setpoint
command will be determined by the parameters in the control.
Rate command will be 0 - 100% of the modulation range.
All sensors and limiting devices should be hardwired to the terminal strip on the back of the unit excluding the 0 - 10Vdc signal.
This signal will be sent to the unit via ModBus.
The holding registers will need to be set as follows:
Holding Registers Definition Bit Value (HEX) Action
40001 Configuration 00 04 Set Configuration to read 40003
40003 Rate Command 00 00 Sets Modulation % or Setpoint
For proper hexadecimal conversion of rate percentage, please refer to the Rate and Temperature Conversion section on page 17
of this manual.
NOTE: To ensure proper operation re-send the configuration bits to holding register 40001 prior to issuing a command.
Hot Water Generation
Hot water generation can be accomplished with one of two methods when a Crest boiler is connected to a BAS system, DHW
with direct control, and DHW with remote control.
DHW with direct control:
This is the typical installation with a hot water generator in close proximity to the boiler with the tank thermostat, or tank
temperature sensor, wired to the terminal strip of the unit.
Demand Configuration: ENABLE = ACTIVE; BMS = ACTIVE
In this configuration the unit is controlled by providing an enable signal. The setpoint command will be determined by the
parameters in the control and a rate command through ModBus communications.
The rate command will be 0 - 100% of modulation.
All sensors and limiting devices should be hardwired to the terminal strip on the back of the unit excluding the enable and 0-10V
BMS signal. These signals will be sent to the unit via ModBus.
The holding registers will need to be set as follows:
Holding Registers Definition Bit Value (HEX) Action
40001 Configuration 00 05 Set Configuration to read 40002 & 3
40002 Coils 00 01 Enables unit (00 00 disables unit)
40003 Rate Command 00 ## Sets Modulation % or Setpoint
NOTE: To ensure proper operation re-send the configuration bits to holding register 40001 prior to issuing a command.
For proper hexadecimal conversion of rate percentage, please refer to the Rate and Temperature Conversion section on page 17
of this manual.
ModBus Instructions

16
5 Unit Operation
Cascade
In order to operate the Crest boiler in Cascade with ModBus
communications, configure the leader boiler per the demand
configurations in this manual. Connect the remaining boilers
in the cascade through the normal cascade communications
wiring. Cascade control can then be accomplished
automatically through the leader boiler.
Please note that with ModBus communication connected to
only the leader boiler, total Cascade information can be seen
through the communications link. If you wish to see all the
individual temperatures of each unit in the Cascade, each unit
will have to have a ModBus communication board. However,
each unit can be monitored without the need to control each
one individually.
DHW with remote control:
This installation may or may not have the hot water generator in close proximity to the boiler. Its sensors and thermostat values
are only available through the ModBus communication bus.
To ensure that the Crest boiler can properly respond to a call for hot water generation the following holding registers must be
set in addition to other commands:
Holding Registers Definition Bit Value (HEX) Action
40001 Configuration 00 4A Set Configuration to read 40002, 4 & 5
40002 Coils 00 08 Enables Tank Tstat (00 00 disables unit)
40004 Tank Setpoint 0# ## Sets Setpoint
40005 Tank Temperature 0# ## Passes tank temp from remote sensor
For proper hexadecimal conversion of rate percentage, please refer to the Rate and Temperature Conversion section on page 17
of this manual.
NOTE: To ensure proper operation re-send the configuration bits to holding register 40001 prior to issuing a command.
Monitoring Only
All Crest boilers are equipped with the ModBus communication
board and can be set up to operate with its own internal controls.
If necessary, ModBus can be configured as a monitoring device
by polling the ModBus board for the read only variables.
ModBus Instructions

17
Temperature
The Crest boiler passes temperature data in degrees Celsius.
Also, to accommodate decimal places the decimal value must
be divided by 10.
Here are the conversions to and from Celsius:
T
c= (5/9) * (Tf-32) Tf= (9/5) * Tc+32
Example:
Outdoor temperature from remote sensor on BAS System = 80°F
80°F = 26.7°C
Data that needs to be transmitted is 26.7 * 10 = 267
Decimal Binary HEX
267 100001011 10B
Outlet temperature from unit sensor = 155°F
155°F = 68.3°C
Data transmitted from unit in HEX = 2AB = 683
683 ÷ 10 = 68.3 (°C)
Decimal Binary HEX
683 1010101011 2AB
Rate and Temperature Conversions:
Rate
When issuing a rate command the rate can be communicated
as percent modulation or a desired setpoint, depending on
the setting of the BMS Type in the BMS Setup Menu.
The proper data format for the modulation percentage is the
direct conversion to hexadecimal. This conversion can be
accomplished through online number based converters or
some scientific calculators.
For Example:
To send a desired setpoint, the hexadecimal value must be
determined through linear interpolation of programmable
parameters on the BMS Setup Menu:
- BMS temperature set-point at low analog input
- BMS temperature set-point at high analog input
These variables set the temperature values corresponding to
the minimum and maximum voltage settings of the 0-10 volt
signal. The defaults are as follows:
Rate % HEX
000
20 14
45 2D
60 3C
80 50
95 5F
100 64
PARAMETER DEFAULT
VALUES DEFAULT
Deg C Deg F Voltages
BMS temperature setpoint at
low analog input 21 69.8 2
BMS temperature setpoint at
high analog input 82 179.6 10
For Example:
Send a setpoint of 110°F.
The formula to use for the interpolation is:
Rate Command =
(Desired Setpoint – BMS Temp at Low Analog Input) (High
Voltage-Low Voltage) + Low Voltage
(BMS Temp at High Analog Input – BMS Temp at Low
Analog Input)
From the default values:
Desired Setpoint = 110
BMS Temp at Low Analog Input =68
BMS Temp at High Analog=158
High Voltage =10
Low Voltage = 2
[(110-69.8)(10-2)/(179.6-69.8)] + 2 = 4.92 Volts
(4.92/10) x 100 = 49.2
49 = 31 Hexadecimal
A value of [00][31] in hexadecimal would be written to Holding
register 40003 to issue a command for a 110°F setpoint.
5 Unit Operation (continued)
ModBus Instructions

18
6 Troubleshooting
Should you encounter problems communicating over
ModBus, the following items should be checked in this order:
1. Physical Layer
2. Communications Configuration and Port Settings
3. ModBus Error Codes
4. Unit Status / Blocking / Lockout Codes
Physical Layer
1. Check that all components have power (Boiler, Gateway,
BAS Master)
2. Check all wire lengths. Are any drops too long?
3. Check proper shield grounding
4. Check A, B terminal connections
5. Check for Terminating Resistors (120 ohms)
6. Check for broken wires
Communications
1. Check Dip Switch Configuration of MTR-01 Board
2. Check Baud Rate (9600, 19200)
3. Check Parity
4. Check Slave ID
5. Check Port Setting on Master, Gateway, and Computers
ModBus Error Codes
1. Check ModBus communication for error codes (see page
6 for ModBus Exception Codes)
2. Check ModBus PDU
3. Check Slave ID
4. Check ModBus Command
5. Check Configuration bits for Holding Register 40001
6. Check Commands and data for Holding Registers
40002 - 40007
Unit Status Codes
See Codes in this section
Boiler Status
The Crest boiler displays a boiler state code on the Building
Screen to help aid in troubleshooting. The boiler state
indicates what the boiler is actually doing. This state should
be compared to the command issued and what is expected.
If the boiler state does not agree with the command issued,
check communication and configuration.
Status Codes (Input Registers 30014 and 30023)
2 = Heat Demand blocked due to high absolute outlet
temperature
3 = Heat Demand blocked due to high absolute flue
temperature
4 = Heat Demand blocked due to high absolute Delta T
(Outlet - Inlet)
7 = Heat Demand blocked due to changed Personality Plug
8 = Heat Demand blocked due to Low 24 VAC
9 = Outdoor shutdown
10 = Block due to switch OFF boiler (ON/OFF of Display)
12 = Block due to line frequency
16 = Service function
19 = DHW function Storage Tank
21 = SH function Heat demand from Room Thermostat
22 = SH function Heat demand from Boiler Management
System
23 = SH function Heat demand from Cascade
30 = Heat demand activated by Freeze Protection
32 = DHW Pump Delay
33 = SH Pump Delay
34 = No heat function (after pump delay)
40 = Lockout
Blocking Codes (Input Registers 30015 and 30024)
0 = No blocking
1 = SH blocking
2 = Blocking Due to Low 24 VAC Supply
3 = Blocking due to General block
4 = Blocking MRHL is open
5 = Blocking due to Switched OFF boiler (Display ENTER
switch)
6 = Blocking due to wrong communication of Cascade
7 = Blocking due to High Delta
8 = Blocking due to High Flue Temperature
9 = Blocking due to low 24 VAC supply
10 = Blocking due to General Block
12 = Blocking due to to line frequency
13 = Blocking anti-cycling time
14 = Storage Tank demand Blocked due to Fan problems
15 = No system sensor connected and leader control present
16 = Blocking due to outlet temperature limit
17 = Fan min decreased due to low flame current
18 = Limit max fan speed due to high Delta T
19 = Limit max fan speed due to high flue temp
21 = Blocking due to Switched Off boiler
24 = Blocking due to high temperature rise
25 = Blocking due to high flue temperature
26 = Blocking due to high outlet water temperature
27 = Blocking due to anti-cycling time
28 = Blocking due to changed ID Plug
32767 = Code not present
ModBus Instructions

19
ModBus Instructions
Lockout Codes Description
5 = Analog to Digital converter input had changed too quickly
7 = Rapid Temperature Change on Pre-Mix Sensor 2 (S14)
8 = Rapid Temperature Change on Pre-Mix Sensor 1 (S13)
9 = Rapid Temperature Change on Pre-Mix Sensor 2 (S12)
10 = Rapid Temperature Change on Pre-Mix Sensor 1 (S11)
11 = Analog to Digital converter input is changed too quickly
12 = Rapid Temperature Change on Flue Sensor (S10)
13 = Rapid Temperature Change on Outlet Sensor (S9)
15 = Rapid Temperature Change on System Return Sensor (S7)
16 = Rapid Temperature Change on System Supply Sensor (S6)
17 = Rapid Temperature Change on Tank Sensor (S4)
18 = Rapid Temperature Change on Flue Sensor (S3)
19 = Rapid Temperature Change on Inlet Sensor (S2)
20 = Rapid Temperature Change on Outlet Sensor (S1)
25 = Pre-Mix Sensor 2 (S14)-Short
26 = Pre-Mix Sensor 1 (S13)-Short
27 = Pre-Mix Sensor 2 (S12)-Short
28 = Pre-Mix Sensor 1 (S11)-Short
29 = Flue Sensor (S10)-Short
30 = Outlet Sensor (S9) – Short
32 = System Return Temperature Sensor (S7) – Short
33 = System Supply Temperature Sensor (S6) – Short
34 = Tank Sensor (S4) – Short
35 = Flue Sensor (S3) – Short
36 = Inlet Sensor – Short
37 = Outlet Sensor (S1) – Short
38 = Temperature Measurement Error 2
39 = Temperature Measurement Error 1
45 = High temperature differential between S12 and S14
46 = High temperature differential between S11 and S13
48 = High temperature differential between S3 and S10
49 = High temperature differential between S1 and S9
50 = Internal Error
129 = Large Pre-Mix Temperature High
130 = Small Pre-Mix Temperature High
134 = Louvers Not Open
135 = Louvers Not Closed
137 = Large Blower Proving Switch Not Closed
139 = Large Blower Proving Switch Not Open
140 = Small Blower Proving Switch Not Open
145 = Large Blower Proving Switch Not Closed
146 = Small Blower Proving Switch Not Closed
148 = Large Blower Proving Switch Not Open
149 = Large Fan Speed Too Low
150 = Large Fan Speed Too High
163 = Wrong Personality Plug
164 = Flame Current Circuit Failed
166 = Auto Reset High Limit
167 = Blocked Drain Switch Open
169 = Gas Pressure Switch Open
170 = Low Water Cut-Off Open
177 = Flue Sensor Short
178 = Flue Sensor Open
179 = Inlet Sensor Short
180 = Inlet Sensor Open
6 Troubleshooting (continued)

20
ModBus Instructions
Lockout Codes Description
192 = Outlet Sensor Short
193 = Outlet Sensor Open
201 = Internal Error
204 = Internal Error
205 = Parameters Programmed
206 = Error while programming Parameters
207 = Internal Error
228 = Pre-Mix Sensors Temperature Differential Too High
229 = Flame Failure 2
230 = Small Fan Speed Low
231 = Small Fan Speed High
232 = Flame Failure 1
233 = Ignition Failure
236 = Flue Damper Open
235 = Small Blower Proving Switch Not Open
236 = Small Blower Proving Switch Not Closed
238 = Air Pressure Switch Open
239 = Flame 1 Out of Sequence
240 = External Manual Reset High Limit
241 = Flame 2 Out of Sequence
244 = Large Gas Valve Relay Failure
245 = Small Gas Valve Relay Failure
246 = Internal Manual Reset High Limit
247 = High Flue Temperature
253 = High Combustion Air Temperature
254 = Display Fault
6 Troubleshooting