18
6
Troubleshooting
Should you encounter problems communicating over
ModBus, the following items should be checked in this order:
1. Physical
Layer
2. Communications
Confi guration 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 Confi guration 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
Confi guration 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 confi guration.
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 fl ue
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 fl ame current
18 = Limit max fan speed due to high Delta T
19 = Limit max fan speed due to high fl ue temp
21 = Blocking due to Switched Off boiler
24 = Blocking due to high temperature rise
25 = Blocking due to high fl ue 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