Specifications

52
LP- 276 REV. 9.4.14
When a demand for hot water is received, the control begins the following demand sequence. The boiler first turns on the pump (if it is
not wired to run continuously). Once the pump is running, the control will display FL and wait for the water flow in the system to
increase to an acceptable level determined by the flow switch on the outside of the boiler. (NOTE: This step may happen very rapidly. If
flow is adequate, FL may never display.)
Once flow through the boiler is adequate, the control will measure the supply temperature. If it is below the set point temperature {dd}
minus the supply hysteresis {sh}, the control will ignite the burner. After the burner is lit, the control modulates the firing rate to control
the supply water temperature at the set point temperature plus the supply offset temperature {Installer #4} above the tank set point
temperature {dd}. When the tank temperature is equal to the tank set point temperature, the control will extinguish the burner and run
the combustion fan to purge gasses from the combustion chamber. In addition, the pump will run for a pump post purge interval. The
control will then be in standby, waiting to process the next demand for heat.
During this process, the control will extinguish the burner if it senses a dangerous or unsafe condition. If the control determines that a
dangerous or unsafe condition has occurred, the control may lock out the boiler and prevent it from igniting until a maintenance person
diagnoses the problem, repairs it, and resets the control. In the event that the control goes into lockout, it will show a diagnostic code on
the display, illuminate the LED fault indicator, and close the alarm relay contacts to aid in recognition of the condition, diagnosis, and
repair.
F. SETTING UP A CASCADED SYSTEM
If the boiler is part of a cascaded system the operation is somewhat different. The control of each boiler in a cascaded system
completes its own power up system check as described above. One of the boilers in the cascade system is designated as the master
boiler. After the master boiler completes its power up sequence, it checks the communication bus to see if any other boilers are
present. If other boilers are present, the master control determines these follower boiler addresses. The master boiler control will
recheck the bus every few seconds as long as it is powered up to update the status of the connected boilers. The control in the master
boiler processes all heat demands and dictates which of the follower boilers should light and what firing rate the followers should try to
achieve.
When the master boiler receives a demand for heat, it determines which boiler is first in the firing sequence and sends that boiler a
command to begin a demand sequence. That boiler will then begin a demand sequence as described above. Once the boiler ignites,
the master boiler control will increase the firing rate command to that boiler until the system sensor temperature is at the tank set point
temperature plus the supply offset temperature {Installer #4}, or that boiler is at high firing rate. If the command from the master boiler
control gets to the high firing rate of the follower boiler, but the system sensor is below the required temperature, the master boiler
control will then tell the next boiler in the firing sequence to begin its demand sequence. The master boiler control will then begin to
ramp up the firing rate command of that boiler. This process will continue while there is a demand until all boilers in the cascade system
are at high fire or the desired temperature of the system sensor is reached. If the system sensor temperature reaches tank set point
and {Installer #4} before all boilers are at high fire, the master control will modulate the cascade command signal to maintain the system
sensor at tank set point and {Installer #4} until the demand is complete. When the tank temperature is equal to the set point
temperature {dd}, the demand is complete, and the master boiler control will extinguish all boilers that may be lit. If the demand
decreases, the firing rate command and amount of boilers lit will decrease exactly opposite as described above.
Whenever the master boiler control needs to fire a follower boiler, it sends a firing rate command to that boiler. The follower boiler will
respond to the command until its supply sensor temperature gets to be 5
o
F above the tank set point temperature plus the supply offset
temperature {Installer #4}, at which point the individual boiler will modulate on its own so as not to overheat. As a result, it is not
uncommon to see the cascade output at maximum but individual boilers firing at less than their maximum firing rate.
G. LOCKOUT CONDITION
If any boilers, including the master boiler in the cascade system, are in a lockout condition, the master control will recognize the lockout
condition and skip over the boiler in the firing sequence. Each boiler in the cascade system is responsible for its own safety functions.
So, if any individual boiler control senses an unsafe condition, it will extinguish the burner and, if necessary, go to a lockout condition. In
this way, every boiler in the system has its individual safety controls intact and operational, even if the firing of the boiler is under control
of the master boiler.
In the event that the system sensor fails, all boilers in the system will ignite simultaneously when there is a demand, and each boiler will
individually regulate firing rates to maintain the master set point temperature (tank set point plus {Installer #4}) at the individual supply
sensors built into the boiler. If this should happen, the master boiler will display an E03 fault code, indicating that the supply sensor has
failed.
H. CASCADE SYSTEM PROGRAMMING
1. If the boiler is used alone, skip this section.
2. Programming the Master Boiler:
a. Make sure there is no demand for heat being supplied to the boiler.
b. Apply power to the boiler.
c. Enter the installer menu following instructions in Part 10 of this manual.