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i. Operation
Table 2: Frost Protection
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, Header
Sensor 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.
2. High Differential Temperature Limit
The Control monitors the temperature difference
between the return and supply sensors. If this difference
exceeds 43°F (23.9°C) the control begins to reduce the
maximum blower speed. If temperature difference
exceeds 53°F (29.4°C) a forced boiler recycle results.
If the temperature difference exceeds 63°F (35°C) the
control will shut the unit down. The unit will restart
automatically once the temperature difference has
decreased and the minimum off time has expired.
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: flow
switch, thermal fuse and sump pressure 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.
7. Ignition Failure
The Control monitors ignition using a burner mounted
flame sensor. In the event of an ignition failure, the
control retries 5 times and then goes into soft lockout
for one hour.
8. Central Heating System Frost Protection
When enabled, Frost Protection starts the boiler and
system pump and fires the boiler when low outside air
and low supply water temperatures are sensed. The
Control provides the following control action when
frost protection is enabled:
Device
Started
Start
Temperatures
Stop
Temperatures
Boiler Pump
Outside Air < 0°F (-18°C)
Supply Water < 45°F (7.2°C)
Outside Air > 4°F (-16°C)
Supply Water > 50°F (10°C)
Boiler
Supply Water < 38°F (3.3°C)
Supply Water > 50°F (10°C)
FROST PROTECTION NOTE
The Control helps provide freeze protection for the boiler
water. Boiler flue gas condensate drain is not protected from
freezing. Since the Control only controls the system and
boiler circulators individual zones are not protected. It is
recommended that the boiler be installed in a location that is
not exposed to freezing temperatures.
