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Fig. 31: Operating Control
Low Water Cut-Off (Optional)
The low water cut-off automatically shuts down the
burner whenever water level drops below the level of
the sensing probe. A 5-second time delay prevents
premature lockout due to temporary conditions such
as power fluctuations or air pockets.
Fig. 32: Low Water Cut-Off
High and Low Gas Pressure Switches
The low gas pressure switch (standard on models
989B–2339B, optional on models 399B–899B) con-
nection mounts upstream of the gas valve to ensure
that sufficient gas pressure is present for proper regu-
lator performance. The low gas pressure switch
automatically shuts down the heater if gas supply
drops below the factory setting of 5.0 in. WC for natu-
ral gas, and 10.0 in. WC for propane gas.
The high gas pressure switch (optional) connection
mounts down-stream of the stage-1 gas valve. If the
gas pressure regulator fails, the high gas pressure
sheets supplied with your heater paperwork. See the
General Safety Section for safety precautions con-
cerning domestic hot water applications.
Fig. 33: High/Low Gas Pressure Switch
Fig. 34: Fan-Proving Switch
Fig. 35: Blocked Vent Switch
switch automatically shuts down the burner. The high
gas pressure switch automatically shuts down the
heater if gas manifold pressure rises above the recom-
mended setting of 5.0 in. WC for natural gas, and 11.5
in. WC for propane gas.
38
NOTE: Some jurisdictions may require two high gas
pressure switches on models 1529B–2339B due to
two ignition modules.
NOTE: The wiring diagrams in this manual show all
standard options. Refer to the large wiring diagram
provided with your heater for options installed on
your specific unit(s).