Sequence Of Operation - PEERLESS Stainless Steel Gas Boilers Installation, Operation & Maintenance Manual

Figure 6.5:Boiler Control Board Factory Wiring
C. SEQUENCE OF OPERATION
1. When power is first applied to the control, the
control will initially run through a self-diagnostic
routine, and then go into its operating mode. The
green LED light will pulse in a dim to bright
sequence indicating a normal operating mode. If
there is no call for heat, the control will go into the
idle state.
2. If the thermostat is calling for heat, the control will
apply power to the circulator pump. If the control
determines the appliance water temperature is below
the temperature dial set point value less the
switching differential, the control will initiate a
heating cycle.
3. The control then performs selected system diagnostic
checks. If all checks are successfully passed, a 5
second pre-purge cycle is initiated (blower on max
speed).
4. When the pre-purge period is complete, power is
applied to the spark ignitor for a 6 second trial for
ignition. If a flame is not verified during the trial-for-
ignition, the gas valve is immediately closed, and the
control will return to step 2. If after three trials a
flame is not verified, the control will go into lockout
mode. If a flame is confirmed, the control enters the
heating mode.
5. When water temperature reaches the temperature
dial set point plus 10° F (or if the thermostat call-for-
heat is satisfied), the gas valve is closed and the
control enters a 4 second post-purge (blower on max
speed). NOTE: IF THE THERMOSTAT IS STILL
CALLING FOR HEAT, THE CIRCULATOR PUMP
WILL CONTINUE TO RUN UNTIL THE
THERMOSTAT CALL FOR HEAT IS SATISFIED.
6. When post-purge is complete, the control enters the
idle state while continuing to monitor temperature
and the state of other system devices. If a call-for-
heat is received, the control will automatically return
to step 2 and repeat the entire operating cycle.
During the idle state and heat state, if the control
detects an improper operating condition for external
devices such as the high-limit switch, the green LED
on the control will flash an error code sequence.
7. During the call for heat the boiler control board will
continually monitor the return and supply water
temps in relation to the temperature dial set point
and the differential switch setting. The control board
will use this input to modulate the blower speed. The
blower coupled with the gas valve venturi system will
modulate the premix air/gas input to the burner. The
gas valve and venturi system provide the optimum
gas/air ratio through the full burner modulation.
ELECTRICAL
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