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110772-01 - 5/20
CL
Installation & Service Manual
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 floor
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 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.
It is recommended that the LWCO control
is installed above the boiler to provide the
highest level of protection. However, where
the LWCO control is approved by the LWCO
control manufacturer for installation in a high
boiler tapping of a water boiler, the use of the
listed LWCO control is permitted when it is
installed according to the LWCO manufacturer's
instructions.
What Kind
Typically, in residential applications, a probe type
LWCO is used instead of a float 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 in the supply or return piping, as shown
below.
LWCO Location
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 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 configurations. The 120 VAC configuration
must be applied to 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 servicing the
boiler as shown below.
Appendix -
Aftermarket Low Water Cut Off (LWCO)
WARNING
DO NOT ATTEMPT to cut factory wires to install an aftermarket Low Water Cut Off (LWCO). Only use
connections specifically identified for Low Water Cut Off.
In all cases, follow the Low Water Cut Off (LWCO) manufacturer's instructions.
!
