High-Limit Thermostats
©Aqua-Hot®
250-D03 Diesel Series Service Manual
REV 220302
p. 26
Troubleshooting Procedure:
1. Locate the high-limit thermostats (see Figure 41).
2. Disconnect the burner thermostats using the information
below:
• Wires #32 and jumper (left) or wires #33 and jumper
wire (right)
3. Place a jumper wire between the two wires on the harness
to bypass the high-limit thermostat. Check the Aqua-Hot for
normal operation.
4. Disconnect the DC high-limit thermostat wires, then, using
an ohmmeter, check the thermostat for continuity.
5. If continuity does not exist, depress the button in the center
of the thermostat to reset. Reset for continuity.
6. If the thermostat at this point still does not have continuity,
follow the instructions in this section to replace the
thermostat.
Replacement Procedure:
1. Ensure that the Aqua-Hot has been completely shut down,
all power sources disconnected, and the unit is allowed to
cool completely before continuing.
2. Remove the two wires from the defective high-limit
thermostat.
3.
Using a ⅝” socket or crow’s foot, remove the defective
high-limit thermostat from the face of the tank.
4. Install the replacement high-limit thermostat into the port
on the face of the boiler tank and finger-tighten into place.
5. Reconnec
t Jumper wire and wire #32 (left) and/or wires
#33 and jumper wire (right)
to the high-limit thermostat
which has just been replaced.
6. Test for normal operation.
Burner High-Limit Thermostats
Introduction:
The burner high-limit thermostats serve as a safety measure
in the event that the burner continues to operate after the
maximum operating temperature (215°F) has been reached.
If the system reaches an over-temperature condition by
interrupting the fuel solenoid, preventing diesel fuel from
entering the combustion chamber.
Begin troubleshooting the High-Limit Thermostats if the
following conditions have occurred:
• The fuel solenoid fails to operate.
Troubleshooting Guidelines:
The following conditions must be met before the DC High-
Limit Thermostat(s) can be diagnosed, and if necessary,
replaced.
•
The fluid expansion bottle is filled to at least the “COLD”
mark.
• Verify that all in-line fuses are functional.
• Ensure that the unit is completely cool.
• Ensure that DC electrical power is supplied to the Aqua-Hot.
• Ensure that AC electrical power is supplied to the Aqua-
Hot’s electric element.
If any of the above conditions are not met, correct them before
continuing with troubleshooting. Results of the troubleshooting
procedure cannot be verified if the conditions listed above are
not fulfilled.
Failure to disconnect all power supplies and/or allow
the unit to cool before servicing could cause serious
damage or personal injury.
NOTE:
If the high-limit thermostat continues to trip,
troubleshoot the ETS module and verify that the boiler tank
is full of antifreeze and water heating solution.
Figure 41
NOTE:
Bypassing the high-limit thermostats is for testing
ONLY and must
not
be used as a substitute for normal
operation.
Left High-Limit Thermostat
Right High-Limit Thermostat
