Appendix A - Low Water Cut Off - New Yorker AP-490U Installation, Operating And Service Instructions

APPENDIX A: LOW WATER CUT OFF (LWCO) ON HOT WATER BOILERS
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.
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.
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.
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
to the supply or return piping, as shown below.
Select the appropriate size tee using the LWCO
manufacturer's instructions. Often, the branch
LWCO Location
When
Where
WARNING
connection must have a
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.
LWCO's are available in either 120 VAC or 24 VAC
configurations. The 120 VAC configuration 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.
minimum
diameter to
How to Wire
Wiring of Typical LWCO
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