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Feeder Wiring for Boilers Equipped with McDonnell & Miller #67 Low Water Cut-offs
Figures 14a and 14b show feeder wiring for McDonnell & Miller #101A, McDonnell & Miller WF2-U-24 and Hydrolevel VXT-
24 feeders on boilers equipped with #67 low water cutoffs. The following points apply to all feeder wiring to #67 low water
cut-offs:
• Use a separate transformer to power the feeder. Do not use the transformer on the boiler.
• It is not necessary to touch any of the 24 volt factory boiler wiring when connecting a feeder to a #67 equipped
boiler.
• Do NOT install a jumper between terminals 2 and 3 on the #67 low water cutoff.
Indirect Water Heater Wiring
Figure 15 shows field wiring for an indirect water heater. A Honeywell R845A or equivalent DPST relay and transformer is
required. The high limit described in Part IX must also be supplied by the installer. A call for heat from the indirect water
heater thermostat will energize the relay making both sets of contacts. One set of these contacts then energizes the circulator.
The other set of contacts will make the “T” and “T” contacts on the burner primary control, firing the burner. If the boiler
water temperature exceeds the high limit setting of 180F, the high limit will open the “T” - “T” circuit and the burner will shut
down.
If there is a call for space heat, the heating thermostat will make the “T”-”T” circuit and the boiler will fire without regard to
the status of the indirect water heater. The low water cut-off and pressure limit control will interrupt 120 volt power to the
burner in the event of a low water or excessive pressure condition.
FIGURE 14a: WIRING MCDONNELL & MILLER 101A OR TWO-WIRE HYDROLEVEL VXT-24 FEEDER TO BOILER
EQUIPPED WITH #67 L.W.C.O.
CAUTION
DO NOT INSTALL
JUMPER BETWEEN 2 & 3
ON #67 L.W.C.O.
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