Dunkirk Q90-125, Installation, Operation & Maintenance Manual, Page: 20 / 44

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This section provides a brief description of the key controls
and accessories found in this boiler.
See, “Troubleshooting,” page 33 in this installation manual
for detailed sequences of operation and troubleshooting
procedures. See the separately provided “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 high effi ciency gas boilers that
monitors all safety controls and which controls the
operation of the combustion air blower, circulator pump,
burner, and a combination hot surface igniter/fl ame sensor.
This controller is not intended for use with a vent damper.
This controller is mounted on the control panel inside the
boiler and contains fi ve diagnostic indicator lights.
Gas Control Valve
The electronic 24 volt gas control valve contains a 1:1
gas/air pressure regulator to control gas fl ow to the main
burner of the appliance, is suited for both natural and LP
gas, and is rated in accordance with ANSI Z21.21 - latest
revision and CGA-6.5-M95.
Hot Surface Igniter
The 120 volt hot surface igniter heats up to 1800°F to
initiate combustion 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
fl ame by fl ame rectifi cation. In the event of a lack of fl ame
signal on three consecutive trials for ignition, the IBC will
lock out. The “Valve” and “Flame” diagnostic indicator lamps
(see Figure #16) will blink indicating the failure mode as a
lack of fl ame 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” x ½”
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 fi eld
adjustable and may be set anywhere between 100°F and
200°F. The fi eld setpoint adjustment for each installation
depends on heating system requirements. The aquastat
automatically resets when the boiler water temperature drops
20°F below the set-point value. This reset value can be fi eld
adjusted within a range of 5-30°F.
NOTICE
Maximum set-point of the aquastat must not
exceed 200° F.
Casting Temperature Safety Switch
In the event of lack of or loss of water in the boiler, the
casting temperature safety switch (230°F set-point)
installed on the top of the aluminum boiler section behind
the supply piping shuts off the boiler by shutting off power
to the 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 fi lled with water before resetting this switch.
NOTICE
Never run cold water into a hot, empty boiler.
CONTROLS AND ACCESSORIES
Figure 15 -Gas Valve
Figure 16 - Indicator Lights