Low-Temp Cutoff Thermostat
©Aqua-Hot®
250-D03 Diesel Series Service Manual
REV 220302
p. 27
Low-Temperature Cutoff Thermostat
Introduction:
The Low-Temperature Cutoff Thermostat (LTCO) operates
the domestic hot water priority system by blocking the interior
heating feature when domestic hot water is being used. This
ensures that even heat is provided for domestic hot water, which
avoids the possibility of cold water pockets during showers
and other heavy-load applications. Ensure the Aqua-Hot is up
to temperature before troubleshooting the Low-Temperature
Cutoff Thermostat.
Troubleshooting Condition:
This thermostat should be diagnosed if there is a lack
of interior heat or hot water, and the tank is up to operating
temperature.
Troubleshooting Procedure:
Use the following troubleshooting procedure to diagnose the
Low-Temperature Cutoff Thermostat.
1. Verify the following before troubleshooting the low-
temperature cutoff thermostat.
• The ETS module is calling for heat
• The interlock switch is depressed
•
The overflow bottle is adequately filled
• The high-limit thermostats are not tripped
• The fuses are all functional
2. Determine if the unit is ready to provide heat by verifying
that the LCD screen shows the LTCO status properly.
• Verify that the Aqua-Hot is at operating temperature
between 155°F and 185°F by using a meat
thermometer secured to the tank face.
• Verify that domestic hot water is not being used.
• The display screen should display “INT HEAT”.
Figure 42
3. If the ‘Low-Temperature Cutoff Status” display shows
HOT WATER when no hot water is running, complete the
following:
• Disconnect wire J4-1 and J4-2 from the low-
temperature cutoff thermostat.
• If the LTCO status does not change from HOT
WATER to INT HEAT after disconnecting the low-
temperature cutoff thermostat, contact Aqua-Hot
Heating Systems for assistance in diagnosing this
issue.
Lack of Hot Water
1. If the LTCO display shows INT HEAT when domestic
water is being used or when the Aqua-Hot falls below
operating temperature, complete the following:
• Using a temperature sensor, verify that the LTCO
thermostat is below 90°F.
• Inspect the wiring to ensure that the Aqua-Hot is
wired properly and that the LTCO thermostat has
not been disconnected.
2. Disconnect both wires from the Low-Temperature Cutoff
Thermostat. Using a jumper wire, connect these two
wires together.
3. With the jumper wire installed, check the RV for hot water
availability. If after jumping these wires together and
hot water has been established, the Low-Temperature
Cutoff Thermostat will need to be replaced.
Figure 43
