38-13-60
 ú ú 01 Page 2 ú Feb 15/98
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747-400
MAINTENANCE MANUAL

 3. Operation (Fig. 2)
_________
 A. Functional Description
 (1)  Each lavatory compartment water heater is equipped with an ON-OFF switch. The switch is normally positioned to ON for service and the heater cycles automatically until the switch is placed to OFF. In the normal ON position, the heater element is energized until a preset temperature is reached at which time the heat cycle switch opens to de-energize the heating element. As hot water is replaced by cold water through use, the temperature drops, causing the heat cycle switch to close to energize the heating element again. The heat cycle switch regulates the water temperature to approximately 125°F. In event the heat cycle switch should stick in the closed position, the overheat switch opens when the temperature reaches approximately 195°F which de-energizes the heater element. When the overheat switch opens, the indicator light goes out. An overheat condition requires replacement of the malfunctioned heater. In event the lavatory compartment shutoff valve is closed and the pressure in the heater should reach approximately 140 psi, a pressure relief valve opens to relieve the pressure to 130 psi.

ON-OFF LIGHT

SWITCH
Lavatory Water Heater Simplified Circuit
Figure 2

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 ú ú 02 Page 3 ú Feb 15/98
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C23671
A
747-400 MAINTENANCE MANUAL
 WATER HEATER - REMOVAL/INSTALLATION
___________________________________
 1.  General_______
 A.  This procedure includes two tasks:
 (1)  
The first task is the removal of the lavatory water heater (heater).

 (2)  
The second task is the installation of the heater.

 B.  The installation task of the heater includes a functional test and water leak check of the heater.
 C.  The heater is in the lavatory sink cabinet directly below the lavatory basin.
 TASK 38-13-61-004-001
 2.  Lavatory Water Heater Removal (Fig. 401)_____________________________
 A.  Standard Tools and Equipment
 (1)  Container - 1 gallon
 B.  References
 (1)  IPC 38-13-01
 C.  Access
 (1)  Location Zone 224 Upper Deck Crew Rest Body Sta 385 to 632, Right
 D.  Procedure
 S 864-002
 (1)  
Open this circuit breaker and attach a DO-NOT-CLOSE tag:

 (a)  P415 Main Distribution Center - Right Panel 1) 415H27 LAV WTR HTR UPPER DECK U21

 (2)  
Remove the access panel for the sink cabinet.

 (3)  
Close the lavatory water shutoff valve.

 S 864-006

 (4)  
Open the hot water faucet to release the pressure on the heater and water lines.

 (5)  
Disconnect the electrical connection.

 S 014-028
 S 864-004
 S 034-007
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 38-13-61
 ú ú 01 Page 401 ú Oct 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

WATER
HEATER

SEE A

LATCH ACCESS PANEL
SWITCH
OUTLET LINE
ELECTRICAL CONNECTOR
LAVATORY WATER HEATER
A
Water Heater Figure 401
C23687
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747-400 MAINTENANCE MANUAL
 S 034-008
 (6) Disconnect the inlet and outlet water lines.
 NOTE: Use a container to catch the water from the heater and the
　
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