48
Figure 20: Wiring Diagram, Steam, McDonnell & Miller PS-801 Probe LWCO for Beckett Burners
BOILER SEQUENCE OF OPERATION WITH PROBE LWCO
When the thermostat calls for heat, it energizes the cad cell primary control, bringing on the burner. The burner will
operate in the following sequence: Prepurge for the fi rst 10 seconds; fi re until the thermostat is satisfi ed or the limit
setting on the high limit is reached; post-purge for the last 10 seconds. When the high limit control restores the circuit
on a drop in pressure, the burner will start if the thermostat is still calling for heat.
The probe low water cut-off will shut down the burner after a 10-15 second delay, if the water level in the boiler drops
below the probe level.
The probe low water cut-off will reset and restart the burner with a call for heat a few seconds after the water is re-
turned to its normal level.
On burner start, if the cad cell does not see fl ame within approximately 15 seconds, primary control will shut burner
down and enter into a recycle mode, after 60 seconds burner will restart and repeat trial for ignition. If after three
(3) trials for ignition, fl ame is not detected, control will enter into restricted mode and must be reset manually before
burner can be restarted.
When there is no demand for heat, the operating control will maintain the boiler water temperature at the selected set-
ting for proper operation of the domestic water heater, if equipped with optional tankless heater.
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