U.S. Boiler Company SERIES 3, Installation, Operating And Service Instructions

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APPENDIX h – OPERATION
Boiler Sequence of Operation
NORMAL OPERATION
1.
The boiler is equipped with an Intelligent
Hydronic Control (control). This control
replaces the traditional separate ignition
control, high limit switch and circulator relay
and adds energy saving thermal purge
features. Energy is saved by starting the
circulator and delaying the burner start when
there is residual heat available in the boiler.
2.
The boiler’s sequence of operation is shown
in Table 4.
3
. When the thermostat calls for heat the
control starts the system circulator and
the thermal purge (circulator Pre-purge
time) begins. If the time is completed or
boiler temperature is less than the Start
Temperature (140°F default) the start
sequence continues by energizing the vent
damper. Once the vent damper is fully open
the ignition sequence is started allowing gas
flow and ignition of the burners.
4.
If the thermostat is not satisfied and the
operating setpoint is reached the system
circulator will continue to operate and the
burner will stop. When the boiler water
temperature drops below the setpoint less
the differential setting the burner will restart.
5.
After the thermostat is satisfied the burner
and circulator are stopped and vent damper
is closed.
6.
When an indirect water heater aquastat call
for heat is wired to the DHW input the control
starts the Domestic Hot Water circulator
and, if the boiler temperature is less than the
operating setpoint less differential, the vent
damper is energized without delay. Once
the vent damper is fully open, the ignition
sequence is started allowing gas flow and
ignition of the burners.
BOILER FAULT
In the event the boiler fails to start, the control
provides status information to help determine
the cause of the problem. Table 5 provides
a list of boiler status codes that are reported.
Refer to the Troubleshooting Section for more
information.
Status Codes displayed in
STA
Mode
Status
STA
Description
Standby
(Burner off
Circulator off)
1
No call for heat detected
Circulator
Pre-purge
(burner off
circulator on)
1
Either condition is true:
a. Call for heat detected and boiler
temperature higher than operating
setpoint.
b. Call for heat detected and boiler
temperature higher than Start
Temperature (140°F default) and
Circulator Pre-purge Time has not
expired.
Self Test
17
Control internal checking
Drive Damper
Open
18
The damper is energized. The control
is waiting for the damper switch to
close. If the damper end switch
doesn't close within 60 seconds, the
control goes to
STA 20
Pre-purge
4
Damper is open for a 2 second delay
Spark
6
The pilot fuel valve is open and
sparking is started.
Flame
Proving
7
The main fuel valve is open and flame
is being proven.
Running
8
The burner runs until the call for heat
is satisfied or the operating setpoint is
reached.
Status Codes displayed in
STA
Mode
Status
STA
Description
Retry /
Recycle
Delay
10
If the burner fails to light off (no flame
signal), it waits 5 minutes and retries
or if the control loses flame signal
during running, it will wait 10 seconds
and then recycle.
Soft Lockout
13
System is shutdown and will restart
following a one hour enforced delay.
Hard Lockout
14
System is locked out. A manual or
power reset is required to be able to
light off again.
Limit Open
15
There is a call for heat from the
thermostat, but a Safety Limit is open.
Flame
Present Out
of Sequence
16
Flame signal is still present when
expected to be 0 (no flame).
Damper
Failed to
Open
20
The damper is still energized and the
damper end switch has not closed.
Table 5: Sequence Fault
Table 4: Sequence of Operation