Safety Interlocks - PEERLESS Pinnacle PI-399 Installation And Operation Manual

d) Once the pre-purge cycle is complete, the fan
speed decreases to the programmed ignition
speed.
e) The main gas valve is then energized to allow gas
to mix with the combustion air.
f) If the main flame is not detected in 5 seconds, the
gas valve closes and the combustion fan goes into
post-purge. Otherwise, the combustion fan stays at
the ignition speed for the length of the flame
stabilization period. (10 to 25 seconds).
g) After the flame stabilization period is complete, the
combustion air fan ramps down to its low fire
setting. Then the boiler will begin to modulate
depending on the supply temperature to maintain
the set point temperature.
h) As the supply temperature approaches the set
point, the combustion control will reduce the input
rate. The supply temperature will continue to
climb to about 7°F above the boiler set point
before it cycles off.
i) The differential is applied from this point. For
example if the boiler set point is at 180°F with a
10°F differential, the supply temperature will reach
187°F before shutting down. It will not re-start
until the supply temperature drops below 177°F.
Figure 6.4: Component Wiring
j) If an indirect limit is connected between two light
blue (DHW) wires, the boiler will run the same as
described in 2.a through i except it will use the
Indirect (DHW) setpoint.
C. SAFETY INTERLOCKS
1. Low Water Pressure Limit Switch: This boiler is
intended to operate at pressures exceeding 10 psig. If
the water pressure drops to below 10 psig, there is a
water pressure limit switch that interrupts boiler
operation and displays the message "PR0" on the
display module. The combustion air fan completes a
post-purge in this event. Once the low water pressure
condition is corrected the boiler will reinitiate a
heating cycle if a call for heat remains.
2. High Water Temperature Limit Switch: The boiler is
equipped with a limit switch that will interrupt the
heating cycle and execute a post-purge if the water
temperature increases to above the limit set point of
210°F.
3. High Flue Temperature Limit Switch: The high flue
temperature limit switch will interrupt the heating
cycle if it senses flue gas temperatures above 210°F.
ELECTRICAL
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