McDonnell & Miller MM 286 Series 1575 Low Water Cut-Off - Manual (Page 10)

Green LED does not turn on.
• There may be no power to the unit. Check wiring
connected to ‘H’ and ‘N’ terminals on circuit board.
Verify that the control is being powered when the
boiler power is turned on.
Red & Green LEDs flash alternately every
1/2 second.
• The probes are out of sequence. Check probe
wires and connections.
Red & Green LEDs flash simultaneously every
1/2 second.
• The temperature at the circuit board is higher than
170˚F. Removing the control box cover may cool
the control enough for it to operate. If the control
works with the cover removed, the control box
should then be mounted remotely.
Pump does not turn off when water level is above
shortest probe.
• The probes may be fouled with dirt, scale or rust.
Remove head assembly to inspect probes.
• The wiring connections for the pump may not be
connected properly. Check wiring at terminals.
Pump does not turn on when water level is below
the middle probe.
• The probes may be fouled with dirt, scale or rust.
Remove and inspect probes.
• The wiring connections for the pump may not be
connected properly. Check wiring at terminals.
Burner does not turn off when water level is
below longest probe.
• The probes may be fouled with dirt, scale or rust.
Remove and inspect probes.
• The wiring connections for the burner may not be
connected properly. Check wiring at terminals.
• Make sure the time delay is not causing delay of
burner off.
The 1575 control does not turn off the burner
before the secondary (manual reset LWCO) turns
off the burner.
• The burner off time delay (DOB) may be set for too
long of a delay.
During operation, the burner does not turn off
when the water level is below the longest probe.
• The burner off time delay (DOB) may be set for too
long of a delay.
• The boiler water may be priming or foaming. Clean
boiler water and/or consult with chemical treatment
specialist.
During operation, the burner turns off even when
the pump has turned on or the motorized valve
has opened.
• Pump capacity may not be sufficient or there may
be restrictions in the feedwater piping. Check pump
capacity and piping.
• The motorized valve stroke-to-open time may be
too long. Check valve motor timing.
Troubleshooting
10