Operating Gas Valve Maintenance
⚠ WARNING ⚠
The operating gas valve is the prime safety shutoff. All gas supply lines must be free of dirt or
scale before connecting to the unit to ensure positive closure.
Inspect the operating gas valve, carefully remove any external dirt accumulation, and check wiring connections.
Check the valve annually to ensure that the valve is shutting off gas flow completely as follows:
1. Turn manual valve OFF to prevent flow to gas valve.
NOTE: A manometer (fluid-filled gauge) is recommended rather than a spring-type gauge due to
the difficulty of maintaining the calibration of a spring-type gauge. Use a water column manometer
that is readable to the nearest tenth of an inch.
2. Connect manometer to 1/8-inch output pressure tap on valve (see Figure 28).
3. Turn manual valve ON and heater OFF.
4. Use finger to fully block main burner orifice for several seconds.
5. Observe manometer with orifice blocked. If any pressure is indicated, gas valve is leaking.
6. Replace leaking gas valve before heater is restored to operation.
Pressure Switch Maintenance
If it is determined that the pressure switch (see Figure 27) needs replacing, use only the factory-authorized replacement
part that is designed for the model and size of heater being serviced. Replace the switch in accordance with the
Pressure Switch Replacement section.
NOTE: A unit operating above 6,000 feet (1,830 meters) in elevation requires a high-elevation pres-
sure switch (refer to Pressure Switch Replacement section).
High Temperature Limit Control Maintenance
If it is determined that the high temperature limit control (see Figure 33) needs replacing, use only a factory-authorized
replacement part that is designed for the size of heater. For the approximate limit control location, see Figure 25.
Figure 33. Replaceable Components
Interlock Door Switch Maintenance
If it is determined that the interlock door switch (see Figure 33) needs replacing, use only a factory-authorized
replacement part that is designed for the heater. For the approximate door switch location, see Figure 25.
Transformer Maintenance
Use a voltmeter to verify that there are 24V output from the transformer (see Figure 33). If the transformer is not
functioning, it must be replaced. Use a replacement transformer identical to the factory-installed model. For the
transformer location, see Figure 25.
HIGH TEMPERATURE
LIMIT CONTROL
INTERLOCK DOOR
SWITCH
TRANSFORMER VENT TEMPERATURE
LIMIT SWITCH
DISCONNECT SWITCH
53
I-UEZ (04-21) 1034347-0
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