Energy Tech Laboratories 40 Series ユーザーズマニュアル

 

A 24 VAC LWCO is used primarily for gas fired 
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.

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 filling the system.  
The boiler should attempt to operate once the water 
level is above the LWCO.

 

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.

 

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.

A “tee” is commonly used to connect the probe LWCO 
to the supply or return piping, as shown below.  

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.

 

Select the appropriate size tee using the LWCO 
manufacturer’s instructions.  Often, the branch 

connection must have a 

 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