77
X. Operation
C. Boiler Protection Features (continued)
C. Boiler Protection Features
1. Supply Water Temperature High Limit
The boiler is equipped with independent automatic reset and a
manual reset high limit devices. A supply manifold mounted
limit device provides the automatic reset high limit. The
automatic high limit is set to 200°F (93.3°C). The control
monitors a supply water temperature sensor that is also
mounted in the supply water manifold and an internal, manual
reset high limit. If supply water temperature exceeds 190°F
(87.7°C), the control begins to reduce the blower maximum
speed setting. If the temperature exceeds 200°F (93.3°C),
a forced recycle results. If the temperature exceeds 210°F
(98.9°C), a manual reset hard lockout 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. Flow Switch
For coil-type water boilers requiring forced circulation with
input rating greater than or equal to 400,000 BTU/hr, ASME
Boiler and Pressure Vessel Code requires a flow switch in
lieu of low water cutoff. ALSO ADHERE TO ALL LOCAL
CODE REQUIREMENTS. Contact your local code inspector
prior to installation.
The flow switch is an operating control, which must be used
in conjunction with supply water temperature high limit. It
is factory provided with Apex boilers and must be installed
as part of near boiler piping (see Section VI ‘Water Piping
and Trim’ of these instructions).
The control shuts down the boiler when the water flow in
boiler primary loop is either non-existent or too low. This
ensures the boiler shutdown to prevent boiler overheating.
When water flow is restored to a boiler-specific minimum
flow value (see Table 12 ‘Flow Range requirement Through
Boiler’) the switch will detect the flow and restart boiler
automatically.
If the flow switch opens, the boiler will shut down and an
open limit indication and error code is provided.
4. 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.
5. External Limit
An external limit control can be installed between
terminals 11 and 12 on the low voltage terminal strip. Be
sure to remove the jumper when adding an external limit
control to the system. If the flow switch is installed, any
additional external limit must be wired in series with the
flow switch. If the external limit opens, the boiler will
shut down and an open limit indication and error code
is provided. If the limit installed is a manual reset type,
it will need to be reset before the boiler will operate.
6. Boiler Mounted Limit Devices
The Control monitors individual limit devices: pressure
switch, high limit device, condensate level switch,
Thermal Link, Burner Door Thermostat with manual
reset, flow switch, fuel gas pressure switches (optional)
and external limit (optional). If any of these limits opens,
the boiler will shut down and an individual open limit
indication is provided.
7. Stack High Limit
The Control monitors the flue gas temperature sensor
located in the vent connector. If the flue temperature
exceeds 184°F (84.4°C), the control begins to reduce the
maximum blower speed. If the flue temperature exceeds
194°F (90.0°C), a forced boiler recycle results. If the
flue temperature exceeds 204°F (95.6°C), the control
activates a manual reset Hard Lockout.
8. Ignition Failure
The Control monitors ignition using a burner mounted
flame sensor. In the event of an ignition failure:
• Model APX425 - the control retries 5 times and
then goes into soft lockout for one hour.
• Models APX525, APX625, APX725 and APX825 - the
control retries 1 time and then goes into hard lockout.
Manual reset is required to resume boiler operation.
9. 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 & System
Pump
Outside Air < 0°F (-18°C)
Supply Water < 45°F (7.2°C)
Outside Air > 4°F (-15°C)
Supply Water > 50°F (10°C)
Boiler
Supply Water < 38°F (3.3°C) Supply Water > 50°F (10°C)
Table 26: Frost Protection
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.
Summary of Contents for APEX
Page 57: ...57 VIII Electrical continued Figure 26 Ladder Diagram ...
Page 58: ...58 VIII Electrical continued ...
Page 59: ...59 Figure 27 Wiring Connections Diagram VIII Electrical continued ...
Page 105: ...105 ...
Page 109: ...109 XIII Repair Parts continued APX625 APX725 and APX825 APX825 shown ...
Page 112: ...112 XIII Repair Parts continued APX425 and APX525 ...
Page 114: ...114 XIII Repair Parts continued APX625 APX725 and APX825 ...
Page 122: ...122 ...
Page 123: ...123 ...
