McDonnell & Miller MM 286 Series 1575 Low Water Cut-Off - Manual (Page 2)

2
Electronic Control Unit
Burner Relay Time Delay
The field-adjustable time delay (DOB) helps to
p r event nuisance bu rner shut-dow n . The number
of seconds water needs to be off the longest probe
b e fore the bu rner will shut down can be set
b e t ween 0 and 60 seconds.
Redundant Low Water Cut-Off
When the boiler water drops below the middle
p r o b e, a 3 minute timing circuit will be activa t e d . I f
water does not return to the middle probe within
three minu t e s, the bu rner relay will shut dow n . T h e
Red LED will flash once eve ry second if this
condition occurs.
• Automatic Reset units will automatically reset
when the water level is restored to the middle probe.
N OT E : The timing circuit will automatically reset
if the water level returns to the middle probe within
3 minu t e s.
Redundant Pump Off
The pump relay will be activated, turning the pump
on after water drops below the middle probe. If the
water level is not restored to the top probe within 3
m i nutes the pump relay will be deactivated, shutting
off the pump. After the pump relay is deactiva t e d ,
n o rmal operation is resumed. Water must again
drop off the middle probe to activate the pump
r e l ay. There is no LED signal for this occura n c e.
A d j u s t a ble Pump Diffe r e n t i a l s
The water level positions for turning the pump on
and off and obtaining the needed pump diffe r e n t i a l s
are changed by cutting the length of the middle and
s h o rtest probes.