97
XV. LOW WATER CUT OFF (LWCO)
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A 24 VAC LWCO is used primarily for gas fi red
boilers where a 24 volt control circuit exists within the
boiler. However, a 24 VAC LWCO can only be used
if the boiler manufacturer has provided piping and
wiring connections and instructions to allow for this
application.
How to Test
Shut off fuel supply. Lower water level until water
level is BELOW the LWCO. Generate a boiler demand
by turning up thermostat. Boiler should not attempt to
operate. Increase the water level by fi lling the system.
The boiler should attempt to operate once the water
level is above the LWCO.
Wiring of Typical LWCO
When
A low water cutoff is required to protect a hot water
boiler when any connected heat distributor (radiation)
is installed below the top of the hot water boiler (i.e.
baseboard on the same fl oor level as the boiler). In
addition, some jurisdictions require the use of a LWCO
with a hot water boiler.
Where
The universal location for a LWCO on both gas and oil
hot water boilers is above the boiler, in either the supply
or return piping. The minimum safe water level of a
water boiler is at the uppermost top of the boiler; that is,
it must be full of water to operate safely.
What Kind
Typically, in residential applications, a probe type
LWCO is used instead of a fl oat type, due to their
relative costs and the simplicity of piping for a probe
LWCO.
How to Pipe
A “tee” is commonly used to connect the probe LWCO
to the supply or return piping, as shown below.
LWCO Location
draining the heating system. Many probe LWCO
manufacturers recommend an annual inspection of the
probe.
How to Wire
LWCO’s are available in either 120 VAC or 24 VAC
confi gurations. The 120 VAC confi guration can be
universally applied to both gas and oil boilers by wiring
it in the line voltage service to the boiler (after the
service switch, if so equipped).
The presence of water in a properly installed LWCO
will cause the normally open contact of the LWCO to
close, thus providing continuity of the 120 VAC service
to the boiler.
It is recommended to supply power to the probe LWCO
with the same line voltage boiler service as shown
below.
Select the appropriate size tee using the LWCO
manufacturer’s instructions. Often, the branch
connection must have a
minimum
diameter to
prevent bridging between the probe and the tee. Also,
the run of the tee must have a minimum diameter to
prevent the end of the probe from touching or being
located too close to the inside wall of the run of the tee.
Ideally, manual shutoff valves should be located
above the LWCO and the boiler to allow for servicing.
This will allow probe removal for inspection without
Summary of Contents for V8 Series
Page 6: ...6 Figure 1A V82 thru V89 Water Boiler without Tankless Heater ...
Page 7: ...7 Figure 1B V83 thru V89 Water Boiler with Front Tankless Heater ...
Page 8: ...8 Figure 1C V83 thru V89 Water Boiler with Rear Tankless Heater ...
Page 9: ...9 Figure 1D V83 thru V89 Steam Boiler with or without Tankless Heater ...
Page 33: ...33 Figure 13A Recommended Water Piping for Circulator Zoned Heating System ...
Page 46: ...46 Figure 19A Wiring Diagram Steam Hydrolevel CG450 Probe LWCO for Carlin Burners ...
Page 47: ...47 Figure 19B Wiring Diagram Steam Hydrolevel CG450 Probe LWCO for Riello Burners ...
Page 49: ...49 Figure 20A Wiring Diagram Steam McDonnell Miller PS 801 Probe LWCO for Carlin Burners ...
Page 50: ...50 Figure 20B Wiring Diagram Steam McDonnell Miller PS 801 Probe LWCO for Riello Burners ...
Page 52: ...52 Figure 21A Wiring Diagram Steam McDonnell Miller 67 Float LWCO for Carlin Burners ...
Page 53: ...53 Figure 21B Wiring Diagram Steam McDonnell Miller 67 Float LWCO for Riello Burners ...
Page 55: ...55 Figure 22A Wiring Diagram Water without Tankless Heater for Carlin Burners ...
Page 56: ...56 Figure 22B Wiring Diagram Water without Tankless Heater for Riello Burners ...
Page 58: ...58 Figure 23B Wiring Diagram Water with Front Tankless Heater for Carlin Burners ...
Page 59: ...59 Figure 23C Wiring Diagram Water with Front Tankless Heater for Riello Burners ...
Page 62: ...62 Figure 23F Wiring Diagram Water with Rear Tankless Heater for Riello Burners ...
Page 82: ...82 Bare Boiler Assembly ...
Page 84: ...84 Bare Boiler Assembly Continued ...
Page 86: ...86 Jacket Assembly ...
Page 88: ...88 V83 Thru V89 Steam Boilers Trim and Controls ...
Page 90: ...90 V82 Thru V89 Water Boilers Trim and Controls ...
Page 92: ...92 Beckett AFG Burner ...
