High-Limit Thermostats
High-Limit Thermostats
©Aqua-Hot®
125-DN1 Service Manual
REV 220421
©Aqua-Hot®
125-DN1 Service Manual
REV 220421
p. 23
p. 22
High-Limit Thermostats
Introduction:
The Aqua-Hot is equipped with three resettable High-Limit
Thermostats. These thermostats are in place to prevent the
heater from operating beyond its safe operational threshold.
These thermostats are resettable and easily replaceable.
Begin troubleshooting the High-Limit Thermostats if the
controller issues an overheat fault, or the electric and/or diesel
burner fail to operate correctly.
Troubleshooting Guidelines:
The following conditions must be met before the High-Limit
Thermostats can be diagnosed, and if necessary, repaired.
•
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.
Troubleshooting Procedure:
Locate the high-limit
thermostat which is
suspected of failure
Using a multi-meter, test
for continuity across this
thermostat
Is continuity present
across this thermostat?
Yes
No
Depress the red button in
the center of the high limit
thermostat (Figure 40)
Re-test for continuity
Does the thermostat now
have continuity?
Yes
No
This thermostat is
functioning as intended.
This
thermostat is
functioning as
intended.
Replace this
thermostat
AC High
Limit
Left High
Limit
Right High
Limit
Figure 39
Figure 40
Replacement Procedure:
If it has been determined that one, or multiple high-limit
thermostats need to be replaced, they can be easily replaced
by following the directions below.
1. Disconnect all sources of AC and DC power from the Aqua-
Hot (if the AC high-limit thermostat is the issue, the AC
access cover will need to be removed - see Figure 41).
2. Disconnect the wires which connect to the non-functional
high-limit thermostat.
3.
Using a ⅝” (16mm) wrench, remove the thermostat from
its location on the fluid tank. Reference Figure 42 for the
DC high-limit thermostat removal and Figure 43 for the AC
high-limit thermostat removal.
4. Locate the new thermostat and secure it in place of the old
thermostat
5. Reconnect the disconnected wires as described by the
table below.
High Limit Thermostat
Wires
Left
J6-3 and BOT1
Right
BOT1 and J6-3-HL
AC
AOT1 and AOT2
6. Test the Aqua-Hot for normal operation.
If issues persist, please contact Aqua-Hot Heating Systems for
additional assistance.
NOTE:
The AC access cover will need to be removed if the AC
high-limit thermostat is the issue or needs to be tested. See
the image below.
Figure 42
Figure 41
Figure 43
AC Cover Removal
AC High-Limit Thermostat Removal
DC High-Limit Thermostat Removal (Right)
