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DC High-Limit Thermostat: Right
The DC high-limit thermostats serve as a safety measure in
the event that the diesel-burner continues to operate after the
maximum operating temperature is reached. The high-limit
thermostats allow the current for the diesel-burner to pass
through them until the boiler tank reaches a temperature of
215°F. Should this temperature be reached, the right high-
limit thermostat blocks the current to the diesel-burner's fuel
solenoid, which prevents the diesel-burner from operating.
Troubleshoot the right DC high-limit thermostat if the fol-
lowing condition has occurred:
The fuel solenoid on the diesel-burner fails to operate.
The diesel-burner switch light flashes an 8 fault code.
Troubleshooting:
1. Place a jumper wire between the black (#8) and black
(#21) wires on the diesel-burner's wire harness to by-
pass the right high-limit thermostat. Check the Aqua-
Hot for normal operation.
NOTE: Bypassing the high-limit thermostats is for testing
only and must not be used for the Aqua-Hot's nor-
mal functioning.
2. Disconnect the right DC high-limit thermostats' wires,
then, using an ohmmeter, check the thermostat for conti-
nuity.
If there is no continuity, complete the following:
A. Press the white reset button on the high-limit ther-
mostat, then re-check for continuity.
®
© 2009 Aqua-Hot
375D Hydronic Heating System Service Manual—Rev. A
S
4: A
ECTION
NOTE: If a thermostat with the wires removed, that
has been reset, does not have continuity, follow the
instructions in this section to replace the high-limit
thermostat.
B. Disconnect the wires from the thermostat and re-
check the thermostat for continuity, as well as the
thermostats' individual wires.
If an individual wire does not have continuity, that
wire must be replaced.
Replacement Procedure:
F
AILURE TO DISCONNECT ALL POWER SUPPLIES AND
TO ALLOW THE HEATER TO COOL BEFORE SERVICING
COULD CAUSE SERIOUS DAMAGE OR PERSONAL INJURY
1. Ensure that the Aqua-Hot has been completely shut
down and that all power sources have been disconnect-
ed.
2. Remove the two wires from the defective high-limit
thermostat by pulling firmly on the wires.
3. Using a 5/8 wrench or socket, remove the defective high
-limit thermostat from the Aqua-Hot's boiler tank.
4. Install the replacement high-limit thermostat into the
port on the Aqua-Hot's boiler tank and finger-tighten
only (15 in/lbs).
5. Connect the wires removed from the defective high-limit
thermostat to the replacement high-limit thermostat.
6. Test for proper operation.
Figure 15
-H
C
QUA
OT
OMPONENTS
— Page 28 —
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