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Fig. 18: Wiring Diagram for Steam Boilers with Optional McDonnell & Miller PS-801 Probe LWCO,
Beckett AFG Burner and Controls, with or without Tankless Heater
Fig. 17: Wiring Diagram for Steam Boilers with Standard Hydrolevel CG-450 Probe LWCO,
Beckett AFG Burner and Controls, with or without Tankless Heater
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 until the
thermostat is satisfied or the limit setting on the high limit is reached. 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.
Any of the probe low water cutoffs will shut down the burner after a 10-15 second delay, if the water level in the boiler drops too low.
The Hydrolevel CG-450 and the McDonnell & Miller PS-804-120 low water cutoffs will shut down the burner for 90 seconds every 10
minutes of firing time to allow water level to stabilize. If the water level is too low the burner will not be allowed to restart.
Any of the probe low water cutoffs reset and restart the burner with a call for heat a few seconds after the water is returned to its
normal level.
On burner start, if the cad cell does not see flame within approximately 45 seconds, primary control will lock out on safety and must be
reset before burner can be restarted.
When there is no demand for heat, the operating control will maintain the boiler water temperature at the selected setting for proper
operation of the domestic water heater, if equipped with optional tankless heater.