Controls And Accessories - Dunkirk 90-50 Installation, Operation & Maintenance Manual

This section provides a brief description of the key controls and
accessories found in this boiler.
See the Troubleshooting section (page 47 of the of this installation
manual) for detailed sequences of operation and troubleshooting
procedures. See the Repair Parts Manual for locations of all control
components and accessories described.
integrated boiler Control (ibC)
The Integrated Boiler Control (IBC) is a microprocessor based
controller for a high efficiency gas boiler that monitors all safety
controls and which controls the operation of the combustion air
blower, circulator pump, burner, and a combination hot surface
igniter/flame sensor. This controller is not intended for use with a
vent damper. This controller is mounted on the control panel inside
of the boiler and contains five (5) diagnostic indicator lights.
gas Control Valve
The electrically controlled 24 Volt Honeywell Model VR8205
Combination Gas Control Valve is designed to meet the
requirements for use with hot surface ignition systems found in this
boiler. The valve is piped to the gas/air mixer.
Hot surface igniter
The 120 Volt Hot Surface Igniter heats up to 1800 °F to initiate com-
bustion of the gas in the burner. The igniter is mounted next to the
burner through the gas/air mixer. The igniter also serves as a means
for proving the main burner flame by flame rectification. In the event
of a lack of flame signal on three (3) consecutive trials for igni-
tion, the IBC will lockout. The "VALVE" and "FLAME" diagnostic
indicator lamps (lamp "D" and "E" on the IBC, See Figure 16) will
blink indicating the failure mode as a lack of flame signal. The IBC is
manually reset from lockout by either removing and reestablishing
the thermostat's call for heat, or by turning the service switch OFF,
then back ON.
High limit aquastat Control
The High Limit Aquastat Control determines the maximum boiler
water temperature and also provides a means for protecting the
boiler and heating system from unsafe operating conditions which
could damage the boiler. The aquastat is mounted in the ½" NPT
control well and ¾"x½" bushing on the top of the front boiler
section at the hot water outlet. The aquastat is tied in with the
IBC and is factory set at 180 °F water temperature. The high limit
setpoint is field adjustable and may be set anywhere between 100
°F and 200 °F. The field setpoint adjustment for each installation
depends on heating system requirements. The aquastat automatically
resets when the boiler water temperature decreases (5-30 °F
adjustable differential). The differential can be adjusted with the
(white) Differential Adjustment Wheel on the aquastat and gives the
flexibility for boiler operation. The larger the differential, the longer
the run cycle of the boiler.

ConTrols and aCCessories

draft inducer Temperature safety switch
The Draft Inducer Temperature Safety Switch is a disc thermostat
(180 °F setpoint) located on the induced draft fan outlet port. The
switch protects the inducer and vent pipe from a potential high
temperature condition for the discharging flue gases. This condition
would typically be a result of higher aquastat setting or over firing.
The temperature safety switch automatically resets when the higher
aquastat setting or over firing. The temperature safety switch
automatically resets when the vent temperature decreases. (15 °F
switch differential).
Casting Temperature safety switch
In the event of lack of or loss of water in the boiler, the Casting
Temperature Safety Switch (300 °F setpoint) installed on the top
of the aluminum boiler section shuts off the boiler by shutting off
power to the Integrated Boiler Control (IBC) and causes the Power
Indicator Light to go out. This fault requires manual reset of the
casting temperature safety switch to restart the boiler. Verify that
the boiler is properly filled with water before resetting this switch.
WARNING-Never run cold water into a hot empty boiler.
differential pressure air proving switch/blocked Vent
safety shutoff
All 90 Series Hot Water Boilers come equipped with either one (100
Series) or two (200 Series) diaphragm-type differential pressure
switches. The differential pressure switch monitors air flow by
sensing the differential pressure measured in inches of water (" w.c.).
The pressure switch contacts close when the draft inducer is running.
The closed switch proves there is adequate air flow for combustion.
The pressure switch shuts off the main burner if the differential
pressure is inadequate due to a blocked vent pipe, a blocked air
intake, blocked boiler sections, or a blocked draft inducer. After
five (5) minutes of lack of adequate differential pressure, the IBC
will lock out and the "Purge" indicator light will blink, indicating a
failure to prove adequate combustion air flow or flue gas flow. The
IBC will be automatically reset after fifteen (15) minutes or can be
manually reset from lockout by (a) removing and reestablishing the
thermostat call for heat or (b) by turning the service switch OFF and
back ON again. If the boiler cannot be restored to normal operating
conditions by resetting the control, contact a quallified service
agency to check the heat exchanger flue-ways for blockage.
30
NOTICE
The maximum setpoint of the Aquastat must
not exceed 200 °F.