35
Servicing should only be performed by a Quali
fi
ed Service Technician
FAULT
CAUSE
CORRECTIVE ACTION
Outlet MRHL
The outlet water
temperature has exceeded
the setting of the manual
reset high limit.
• Verify that the system is full of water
and that all air has been properly
purged from the system.
• Verify that the water heater is piped
properly into the system. Refer to
the Instruction Manual for the proper
piping methods.
• Check 120 VAC to water heater
pump motor on a call for heat. If
voltage is not present, check wiring
back to the main control board.
• Replace the main control board if
necessary.
• If 120 VAC is present on a call for
heat and the water heater pump is
not operating, replace the pump.
• If the manual reset high limit has
tripped, check setting of the device.
• Check resistance of water sensors
and compare to the Table 11.1
mentioned on Page 38. Replace
sensor if necessary.
Blower Speed
The actual blower/fan RPM
is 30% lower or higher than
what is being called for.
• Vent/air intake lengths exceed the
maximum allowed lengths. Check for
proper lengths.
• Check for obstruction or blockage
in the vent/air intake pipes or at
terminations.
• Check the wiring connections at the
blower/fan and at the main control
board.
• Replace the blower/fan.
BLOWN FUSE:
• Replace fuse F4 on the control
board. Refer to Page 27 for
additional information.
• Replace the main control board.
Inlet Sensor Open
The inlet water temperature
sensor has been
disconnected or is not
working properly.
• Check the Inlet Sensor and its
associated wiring. Repair or replace
the sensor or wiring if damaged.
• Measure the resistance of the sensor
and compare the resistance to Table
11 on Page 38.
• Replace the sensor if necessary.
Table 10. Troubleshooting Chart - Fault Messages Displayed on UIM (Continued.)
Tank Temperature
68°F
Operating Setpoint
161°F
S t a t u s : O u t l e t M R H L
HELP
RESET
A. O. Smith XP
MENU
Tank Temperature
82°F
Operating Setpoint
135°F
S t a t u s : B l o w e r S p e e d
HELP
RESET
A. O. Smith XP
MENU
Tank Temperature
73°F
Operating Setpoint
185°F
S t a t u s : I n l e t S e n s o r O p e n
HELP
RESET
A. O. Smith XP
MENU