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or the central heat setpoint is reached. Once the heat
demand is satisfied, the operating setpoint reverts to
the value determined by the Outdoor Air Reset settings.
If Boost Time is zero, then the boost function is not
used.
7. Domestic Hot Water (DHW) Setpoint
Upon a DHW call for heat the setpoint is the user
entered DHW setpoint . When DHW has priority the
boiler will modulate in an attempt to maintain the DHW
set-point at the DHW sensor located near the hot water
connection. The factory default for this setting is 120F.
8. Domestic Hot Water Priority (DHWP)
By default, when there is call for both CH and
DHW, the DHW demand takes priority for the first
60 minutes of continuous simultaneous demand.
This means that all boiler output will be directed to
the DHW demand and the boiler will modulate as
needed to maintain the temperature of the domestic
hot water leaving the boiler at the DHW set-point.
Also by default, during this time the system pump
will circulate water through the system even though
no heat is entering the system from the boiler (this
behavior increases the odds that a "micro zone"
demand can be satisfied using the heat in a buffer
tank or elsewhere in the system).
At the end of the priority time, the boiler will divert
its entire output to the CH demand and will revert to
the CH set point as measured at the supply sensor.
At this point all heating of DHW will end until there
is an interruption in either the CH or DHW demand.
The default 60 minute DHW priority time can be
increased to as much as 120 minutes (see "Changing
Adjustable Parameters").
C. Boiler Protection Features
1. Supply Water Temperature High Limit
The control is equipped with internal operating
control and high limit features. The control monitors
a dual element temperature sensor that is mounted in
the supply water manifold and provides UL353 and
UL1998 internal safety algorithms. If supply water
temperature increases above the active setpoint plus diff
above, default 190°F (87.7°C) the boiler is cycled off.
If the temperature exceeds 210°F (98.9°C), a manual
reset hard lockout results. If the boiler is responding
to the internal Multiple Boiler Control Sequencer, or an
External EMS demand and the supply water temperature
increases above 190°F (87.7°C) the control begins to
reduce the blower maximum speed setting and if the
temperature increases to 200°F (93°C) a forced recycle
results. Additionally, if the supply temperature rises
faster than the degrees Fahrenheit per second limit a
soft lockout is activated.
107774-01- 9/17
XIII. Operation
(continued)
2. High Differential Temperature Limit
The Control monitors the temperature difference
between the return and supply sensors. If this difference
exceeds 52°F (29°C) the control begins to reduce the
maximum blower speed. If temperature difference
exceeds 62°F (34°C) a forced boiler recycle results.
The unit will restart automatically once the temperature
difference has decreased and the minimum off time has
expired. If the temperature difference remains above
72°F (40°C) for longer than 3 minutes a manual reset
hard lockout results.
3. Return Temperature Higher Than Supply
Temperature (Inversion Limit)
The Control monitors the supply and return temperature
sensors. If the return water temperature exceeds the
supply water temperature for longer than a limit time
delay the Control shuts down the boiler and delays
restart. If the inverted temperature is detected more
than five times, the boiler manual reset Hard Lockout is
set. This condition is the result of incorrectly attaching
the supply and return piping.
4. External Limit
An external limit control can be installed on the low
voltage terminal strip. Be sure to remove the jumper
when adding an external limit control to the system. If
the external limit opens, the boiler will shut down and
an open limit indication and error code are provided.
If the limit installed is a manual reset type, it will need
to be reset before the boiler will operate.
5. Boiler Mounted Limit Devices
The control monitors individual limit devices: External
Limit, Thermal Fuse, Sump Switch and Boiler Water
Flow Switch. If any of these limits open the boiler will
shut down and an open limit indication is provided.
Additionally, the control monitors an air proving switch.
During the boiler start sequence the control requires
the air proving switch to be in the "open" position
before the blower starts and in the "closed" position
after the blower starts. If the air proving switch is not
in the required position the start sequence is halted or
the boiler is shut down and the open limit indication
is provided. The air proving switch is only required
to be closed during pre-purge. It is normal for the air
proving switch to be open during run mode.
6. Stack High Limit
The Control monitors the flue gas temperature sensor
located in the vent connector. If the flue temperature
exceeds 194°F (90°C), the control begins to reduce the
maximum blower speed. If the flue temperature exceeds
204°F (96°C), a forced boiler recycle results. If the
flue temperature exceeds 214°F (101°C), the control
activates a manual reset Hard Lockout.
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