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sheets supplied with your heater paperwork. See the
General Safety Section for safety precautions con-
cerning domestic hot water applications.
Fig. 32: 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. 33: 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 reg-
ulator performance. The low gas pressure switch au-
tomatically shuts down the heater if gas supply drops
below the factory setting of 5.0 in. WC for natural 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
38
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.
NOTE: Some jurisdictions may require two high
gas pressure switches on models 1529B–2339B
due to two ignition modules.
Fig. 34: High/Low Gas Pressure Switch
Fig. 35: Fan-Proving Switch
Fig. 36: Blocked Vent Switch
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).
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