Install Instructions

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APPENDIX A - LOW WATER CUT OFF (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 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 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 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
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
congurations. The 120 VAC conguration 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.
WARNING
DO NOT ATTEMPT to cut factory wires to install an aftermarket Low Water Cut Off (LWCO). Only use
connections specically identied for Low Water Cut Off.
In all cases, follow the Low Water Cut Off (LWCO) manufacturer's instructions.