Aqua-Hot AHE-100-02S User manual

SERVICE MANUAL
© 2011 Aqua-Hot Heating Systems Inc.
AHE-100-02S

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
Section 1: Introduction to the Aqua-Hot AHE-100-02S
Introduction .................................................................................................................Page 6-7
Danger, Warning, Caution, and Note Box Definitions......................................................Page 6
Section 2: Aqua-Hot Hydronic Heating System Overview
Technical Information ......................................................................................................Page 8
I.D. Label Sample............................................................................................................Page 9
Component Overview.................................................................................................Page 9-10
Aqua-Hot Operational Flow-Chart .............................................................................. ..Page 11
Section 3: Interior Switch Panel
Diesel-Burner Switch.................................................................................................. .Page 12
Electric Element Switch.............................................................................................. .Page 12
Engine Preheat Switch ............................................................................................... .Page 12
Section 4: Exhaust System Requirements
Exhaust System Requirements .....................................................................................Page 13
Section 5: Aqua-Hot Components
Control Thermostat - Diesel Burner..........................................................................Page 14-15
Control Thermostat - Electric Element......................................................................Page 16-17
A.C. High Limit Thermostat ..........................................................................................Page 18
D.C. High Limit Thermostat ..........................................................................................Page 19
Check Valves ...........................................................................................................Page 20-21
Tempering Valve ......................................................................................................Page 22-23
Circulation Pumps C, B & A .....................................................................................Page 24-25
Stir Pump .................................................................................................................Page 26
Engine Preheat Pump ..............................................................................................Page 27-28
Interior Zone Relay - Interior Heat Exchanger Fans/Zone Pumps............................Page 29-30
Electric Heating Element ..........................................................................................Page 31-32
Table of Contents

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
Section 6: Diesel-Burner
Overview ................................................................................................................ Page 33-38
I.D. Plate ......................................................................................................................Page 33
Diesel-Burner Overview ......................................................................................... Page 33-34
Diesel-Burner Operational Flow Chart..........................................................................Page 35
Diesel-Burner Operational Overview ...................................................................... Page 36-38
Section 7: Detaching and Reattaching the Diesel-Burner
Detaching the Diesel-Burner .................................................................................. Page 39-42
Reattaching the Diesel-Burner ............................................................................... Page 43-44
Section 8: Diesel-Burner Components / Trouble Shooting
Troubleshooting Flow Chart ................................................................................... Page 45-49
Motor ...................................................................................................................... Page 50-53
Flame Sensor......................................................................................................... Page 54-55
Ignition Electrodes.................................................................................................. Page 56-57
Fuel Nozzle ............................................................................................................ Page 57-58
Fuel Solenoid ...............................................................................................................Page 59
Fuel Pump.............................................................................................................. Page 60-62
Bearings ................................................................................................................. Page 63-65
Ignition Coil ............................................................................................................ Page 66-67
Controller................................................................................................................ Page 68-69
Section 9: General Troubleshooting
If the Aqua-Hot is Black Smoking .................................................................................Page 70
If the Aqua-Hot is Blue/White Smoking ........................................................................Page 71
If one of the Aqua-Hot’s Heating Zones will not get hot................................................Page 72
If there is a lack of domestic continuous hot water .......................................................Page 73
If there is antifreeze leaking ................................................................................... Page 74-75
Appendix A: Wiring Diagram .........................................................................................Page 76-77
Appendix B: BLEEDING THE INTERIOR HEATING ZONE CIRCULATION PUMP .....................Page 78-82
Appendix C: Fuel Pressure check and Adjustment .....................................................Page 83-86
Appendix D: Extreme Cold Weather Operation............................................................Page 87-88
Appendix E: Aqua-Hot Annual Maintenance ..............................................................Page 89-102
Appendix F: Winterization Process ..................................................................................Page 103
Table of Contents

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 1: INTRODUCTION TO THE AQUA-HOT AHE-100-02S
This service and parts manual is designed to aid
trained and qualified service technicians with
the process of troubleshooting and servicing the
Aqua-Hot AHE-100-02S Hydronic heating sys-
tem.
The Aqua-Hot AHE-100-02S heating system features a 12
Volt-DC powered diesel-burner and a 120 Volt-AC, 1650
Watt electric heating element. These two heating sources are
used in conjunction with an antifreeze/water heating solution
in order to provide a continuous supply of domestic hot wa-
ter, interior/fresh water tank heating, independent interior
zone heating, and engine preheating. Be sure to reference
Figures 3 for a complete component overview.
Please note that all Danger, Warning, Caution, and Note box-
es, appearing as needed throughout this manual, must be
reviewed and adhered to during any service procedure in
order to avoid potential hazards, which could result in injury,
product damage, or property damage.
Should additional assistance be needed, please contact the
technical support department at 1-800-685-4298, Monday
through Friday, between the hours of 7:00 AM and 4:00 PM
Mountain Standard Time.
Danger, Warning, Caution, and Note Boxes:
Danger, Warning, Caution, and Note boxes appear through-
out this manual as a means of alerting the service technician
to important information.
INDICATES THAT PERSONAL INJURY IS LIKELY OR
IMMINENT.
Indicates that serious damage to the heater will occur
and personal injury is possible as well.
Indicates that damage to the heater is possible.
NOTE: Indicates information that requires special atten-
tion by the service technician
Understanding the Aqua-Hot AHE-100-02S Major
Systems:
The basis for the Aqua-Hot heating system’s functionality is
the antifreeze and water heating solution, which is comprised
of water that is distilled, de-ionized, or soft, as well as anti-
freeze. Through this solution’s ability to maintain and trans-
fer heat, the Aqua-Hot’s three major systems: the domestic
water system, engine preheat system, and interior heating
system, are able to function effectively. This antifreeze and
water heating solution is contained within the Aqua-Hot’s
boiler tank and is heated by the diesel-burner when its oper-
ating criteria are met and/or the electric heating element
when its operating criteria are met. In order for the diesel-
burner to be considered as a heating source by the Aqua-Hot,
it must have an adequate fuel supply, receive power from the
fuse block, and be selected as a heating source from the inte-
rior switch panel. In order for the electric heating element to
be considered as a heating source by the Aqua-Hot, it must
receive power from either a generator or from shore power
and be selected as a heating source. Once the antifreeze and
water heating solution achieves operating temperature (as
determined by the Aqua-Hot’s control thermostat), the do-
mestic water system, the engine preheat system, and the inte-
rior heating system are permitted to operate as needed.
Domestic Hot Water System:
When hot water is requested, domestic water from the motor
home’s fresh water tank is transported through a copper coil
around the Aqua-Hot’s boiler tank where heat is transferred
from the heated antifreeze and water heating solution to the
domestic water flowing through the copper coil. The heated
domestic water then flows through the tempering valve to be
mixed with cool water from the fresh water tank to achieve
an appropriate temperature before it flows to the faucet re-
questing hot water.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 1: INTRODUCTION TO THE AHE-100-02S
Engine Preheat System:
The engine preheat system is responsible for heating the mo-
tor home’s engine block in order to make it easier to start-up
when cool weather conditions exist.
When the engine preheat system is activated via the interior
switch, the motor home’s engine coolant is circulated
through a dedicated copper coil in the Aqua-Hot’s boiler
tank, where heat from the antifreeze and water heating solu-
tion is transferred to the motor home’s engine coolant. The
heated engine coolant is then transported back to the engine
where it transfers the heat to the engine to gradually warm it.
Additionally, the Aqua-Hot includes a motor-aide feature,
which uses the circulation of the motor home’s engine to
transport the engine’s coolant from the Aqua-Hot’s boiler
tank to the motor home’s warm engine and back to the boiler
tank. Through this process, the boiler tank is kept heated,
which reduces the time required to bring the tank to operat-
ing temperature for interior heat and continuous domestic hot
water. This motor-aide feature is part of the engine preheat-
ing feature and plumbing system, and requires no action on
the user’s behalf to function.
Interior Heating System:
The interior heating system is responsible for providing heat
to the motor home’s interior in order to maintain the temper-
ature at a comfortable level.
For interior heating, it is the room thermostats that trigger the
Aqua-Hot’s interior heating system. When a thermostat rec-
ognizes that heat is required in a particular area, it sends a
signal to the Aqua-Hot’s corresponding zone relay. The
Zone Relay responds by activating the circulation pump for
that zone, which sends the heated antifreeze and water heat-
ing solution through the Heating Loop corresponding to the
zone requesting heat. The fans on the heat exchangers in the
zone calling for heat are also activated; therefore, as the heat-
ed solution flows over the heat exchanger’s fins, the heat is
transferred to those fins and dispersed into the interior of the
motor home by the fans. Until the thermostat signals that
heat is no longer required, the Aqua-Hot will continue to
send the heated antifreeze and water solution through the
loop, which returns the cooled solution to the Aqua-Hot’s
boiler tank to be re-heated before being sent back through
the loop again. This process continues until the pre-set tem-
perature of the interior is reached, and the interior room ther-
mostat signals the electronic controller that heat is no longer
required.
AC Circuit:
Although the diesel-burner is the primary heating source for
the Aqua-Hot and is necessary for providing continuous do-
mestic hot water, an alternate heat source exists for moderate
temperatures, which functions with an AC circuit. Whenever
the motor home is connected to an AC power source -
plugged into shore power or using a generator, the Aqua-
Hot’s electric heating element has the ability to function in
order to provide heat for the boiler tank.
When the antifreeze and water heating solution falls below
operating temperature (as determined by the control thermo-
stat), the control thermostat closes, and allow AC power to
flow to the electric heating element. When the electric heat-
ing element receives power, it becomes active and supplies
heat to the boiler tank until operating temperature is reached.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 2: AQUA-HOT AHE-100-02S OVERVIEW
Diesel-Burner, Heat Input (Firing Rate)................................................................................................................................................ 50,000 BTU/hr
Diesel-Burner, Fuel Consumption (Continuous Operation) ......................................................................................................................0.50 gal/hr
Heater, Voltage/Maximum Power Consumption ....................................................................................................................12 Volt-DC/60 watts
Electric Heating Element specifications................................................................................................................................120 Volt-AC/1650 watts
Zone Heat Circulation Pump specifications.........................................................................................(3) 12 Volt-DC/12 watt 3.5gpm Flow Rate
Number of Heating Zones ...................................................................................................................................maximum of 3 plus Engine Preheat
Domestic Water Heating Capacity ...........................................................................................................................................continuous/on-demand
Antifreeze Type Used ...............................................................................................................................................................................Ethylene Glycol
Dimensions........................................................................................................................................................................... 18.5”H x 18.5”W x 36.75”L
Dry Weight ...................................................................................................................................................................................... approximately 200lbs.
NOTE: All vehicle installations must comply with the requirements listed in the Recreational Vehicle Industry Association’s
(RVIA) ANSI/NFPA 1192 Handbook for Recreational Vehicle Standards. To receive a copy of this handbook and other perti-
nent RVIA Standards, write to: Recreation Vehicle Industry Association, 1896 Preston White Drive, P.O. Box 2999, Reston,
VA 22090-0999, call them at [phone], or visit them online at www.rvia.org.
Aqua-Hot AHE-100-02S Technical Specifications
Figure 1

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 2: AQUA-HOT AHE-100-02S OVERVIEW
Figure 2

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 2: AQUA-HOT AHE-100-02S OVERVIEW
Figure 3

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
“Diesel Burner”
Switch Turned On
SECTION 2: AQUA-HOT AHE-100-02S OVERVIEW
Heat Source is
selected
“Electric Element”
Switch Turned On
Diesel-Burner heat
source selected by
Diesel-Burner Switch
Electric Heating Element
heat source selected by
Electric Element Switch
Diesel-Burner fires
into the Combustion
Chamber, which heats
the antifreeze and wa-
ter heating solution in
the Boiler Tank
Electric Heating Element
activates, which heats the
antifreeze and water heat-
ing solution in the Boiler
tank
Boiler Tank
heats to 200 °F Boiler Tank heats to 210 °F
Zone Thermostat
calls for heat The Engine Preheat switch on the Interior
of the Motor Home is
activated.
A hot water faucet (e.g.,
kitchen sink, shower,
etc.) calls for hot water
Antifreeze and wa-
ter heating solution
moves through the
Heat Exchangers in
the Zone calling for
heat
Heat Exchanger
fans activate
The Circulation
Pump activates for
the Zone which
called for heat. The
heated antifreeze
and water heating
solution is trans-
ported throughout
the plumbing lines
the that zone.
Heat is transferred to
the Engine Preheat
System
The engine’s coolant
is circulated through
the Aqua-hot’s inter-
nal Engine Preheat
System, where the
heat from the Boiler
Tank is transferred to
the engine’s coolant.
The antifreeze and
water heating solution
within the Boiler Tank
is reheated, as needed,
and continues warm-
ing the engine’s cool-
ant as it circulates
through the Aqua-
hot’s internal Engine
Preheat System
Continuous hot water is
supplied to the faucet
Heat is transferred to
the Domestic Water
System
NOTE: The Diesel-
Burner and/or Electric
Heating Element (as
switched ON) will auto-
matically begin reheat-
ing the antifreeze and
water heating solution
drops below:
175°F - Diesel
184 °F - Electric
The cooled antifreeze
and water heating solu-
tion is returned to the
Boiler Tank to be re-
heated
Heat is transferred into
the Zone calling for
heat

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 3: INTERIOR SWITCH PANEL
Diesel-Burner Switch:
When the diesel-burner switch is in the on position, any time
the control thermostat tells the Diesel Burner that heat is
needed for the boiler tank, the diesel-burner will respond by
firing up and providing heat. A cold boiler tank can expect
to be brought to operating temperature by the diesel-burner
in approximately 20 to 30 minutes. In order to obtain contin-
uous hot water, the diesel-burner switch must be activated.
Electric Element Switch:
When the motor home is plugged into an AC power source
(e.g., shore power, generator, etc.) and the electric element
switch is on, the electric heating element will be used to pro-
vide heat to the boiler tank if the need arises. A cold boiler
tank can expect to be brought to operating temperature by the
electric heating element in approximately 1 to 2 hours. The
electric element, alone, will not be able to provide continu-
ous hot water.
Engine Preheat Switch:
The engine preheat switch activates the engine preheat
pump, which draws the motor home’s engine coolant
through the boiler tank to heat it before returning it to the
engine block to transfer the heat there. The engine preheat
switch does not need to be activated for the motor-aide fea-
ture to work and should be shut off when traveling.
NOTE: If the diesel-burner fails to ignite, the diesel burner
status light will go out, indicating to the customer the burn-
er has gone into a default. To reset the default, the diesel
burner switch must be turned off for 5 seconds and then
turned back on.
Figure 4
NOTE: The Interior switches are supplied by the OEM.
NOTE: If a 12 VDC switch is used to activate the 120 VAC
heating element, there will be a relay, which the 12 VDC
switch will activate to allow 120VAC power to be supplied
to the 120VAC heating element.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 4: EXHAUST SYSTEM REQUIREMENTS
Because the Aqua-Hot’s exhaust is hot and must be kept
away from any heat-sensitive material, the exhaust system
should be checked to ensure that it continues to meet the
following requirements:
 The exhaust must not be directed downward as a fire
could result when parked in dry, grassy areas.
 The exhaust must not terminate underneath the vehicle,
underneath an open-able window or vent, in the awning
area of the motor home (if applicable), or near slide-out
areas.
 The exhaust must be able to freely exit away from the
vehicle without any obstructions.
 1 3/4” - 2” standard automotive-type exhaust piping
should be used with a maximum of two 90-degree pipe
bends and should not exceed 20 feet.
 The 3-inch and 4-inch black-pipe nipples and the ex-
haust elbow - originally supplied with the Aqua-Hot,
must be present.
Figure 5

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
Thermostats
Control Thermostat: Diesel Burner
The Diesel Burner control thermostat is installed onto the
Aqua-Hot’s boiler tank and monitors the temperature of the
antifreeze and water heating solution to determine when it is
at operating temperature and when it requires heat. The Aq-
ua-Hot’s Diesel Burner is considered to be at operating tem-
perature between 175°F and 200°F.
Troubleshoot the control thermostat if one of the following
conditions has occurred:
 There is a lack of hot domestic water and interior heat.
 The Diesel Burner does not operate
 Excessive Blue or white smoke is expelled from the ex-
haust.
Troubleshooting:
1. Turn the diesel-burner switch on the interior switch pan-
el on.
If the Diesel Burner comes on and runs, but there is still
a lack of hot water verify that the control thermostat is
operating within the proper operating temperature range.
A. Using a digital temperature sensor, place the probe on
the tank next to the thermostat. The proper
operating temperature for the diesel burner is
175°F - 200°F.
2. If the Diesel Burner Does not come on and run:
A. Verify that the temperature of the boiler tank has
fallen below the 175°F minimum operating temper-
ature by checking with a digital thermometer.
B. Disconnect the control thermostat’s wires from their
connections, and, using an ohmmeter, check for
continuity.
If there is no continuity, follow the instructions in
this section for replacing the control thermostat.
If continuity exists, complete the following:
a. Inspect the control thermostat’s wiring and
connections.
b. Verify the Diesel Burner’s Controller is send-
ing power to the control thermostat.
Figure 6
190 º F Diesel Burner
Control Thermostat

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
Control Thermostat Replacement Procedure:
FAILURE TO DISCONNECT ALL POWER SUPLIES AND/OR 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. Also, because this replacement procedure will in-
volve the boiler tank and the potential for hot coolant, be
sure the heater has adequately cooled.
2. Disconnect the defective control thermostat’s wires by
separating the quick-disconnect terminals.
3. Using a 1/4” nut driver, unscrew the two screws secur-
ing the control thermostat to the Aqua-Hot’s boiler tank
thermostat mounting bracket.
4. Install the replacement control thermostat into the ther-
mostat mounting bracket and secure with the two screws
previously removed.
5. Inspect the quick connectors on the thermostat wires.
Replace if necessary. Re-Connect the control thermo-
stat’s wires (orange and white).
6. Test the Aqua-Hot for normal operation.
Figure 7
Note: If a screw longer than 1/4” is used to secure the
thermostat in place, it may cause the thermostat mounting
bracket to be pushed away from the boiler tank, and may
result in overheating.
Note: If the control and overheat thermostat wires are
hooked up to the wrong thermostat, the diesel burner will
default every time the heater reaches the maximum operat-
ing temperature.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
Thermostats
Control Thermostat: Electric Element
The Electric Element control thermostat is installed onto the
Aqua-Hot’s boiler tank and monitors the temperature of the
antifreeze and water heating solution to determine when it is
at operating temperature and when it requires heat. The Aq-
ua-Hot’s Electric Element is considered to be at operating
temperature between 185°F and 210°F.
Troubleshoot the control thermostat if one of the following
conditions has occurred:
 There is a lack of hot domestic water and interior heat.
 The Electric Element does not operate
Troubleshooting:
1. Disconnect all power supplies.
2. Remove the thermostat access cover.
3. Verify that the boiler tank’s temperature is below 230°F.
4. Locate the AC control thermostat and remove its wires,
by loosening and removing the screws securing the
wires in place.
5. Using an ohmmeter, check the thermostat for continuity.
If continuity is not present, follow the instructions in
this section to replace the AC control thermostat.
Figure 8
198 º F Electric Element
Control Thermostat
NOTE: For continuous domestic hot water to be present,
the diesel-burner must also be selected as a heating source.
NOTE: The Motor Home’s Manufacturer may not have
installed a switch for the electric element. If that is the case
ensure the A.C. breaker for the Aqua Hot’s electric element
is in the “ON” position.
NOTE: The Motor Home must be plugged into shore pow-
er, or the generator must be operating for the electric ele-
ment to be working.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
Control Thermostat Replacement Procedure:
FAILURE TO DISCONNECT ALL POWER SUPLIES AND/OR 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. Also, because this replacement procedure will in-
volve the boiler tank and the potential for hot coolant, be
sure the heater has adequately cooled.
2. Disconnect the defective control thermostat’s wires by
removing the screws securing the wires to the terminals.
3. Using a 1/4” nut driver, unscrew the two screws secur-
ing the control thermostat to the Aqua-Hot’s boiler tank
thermostat mounting bracket.
4. Install the replacement control thermostat into the ther-
mostat mounting bracket and secure with the two screws
previously removed.
5. Inspect the wires going to the control thermostat Re-
place if necessary. Re-Connect the control thermostat’s
wires and secure in place using the screws previously
removed.
6. Test the Aqua-Hot for normal operation.
Figure 9
Note: If a screw longer than 1/4” is used to secure the
thermostat in place, it may cause the thermostat mounting
bracket to be pushed away from the boiler tank, and may
result in overheating.
NOTE: The Motor Home must be plugged into shore pow-
er, or the generator must be operating for the electric ele-
ment to be working.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
AC High-Limit Thermostat:
The AC high-limit thermostat serves as a safety measure in
the event that the electric heating element continues to oper-
ate after the maximum operating temperature is reached.
The high-limit thermostat allows the current for the heating
element to pass through it until the boiler tank reaches a tem-
perature of 230°F. Should this temperature be reached, the
high-limit thermostat blocks the current to the element,
which prevents it from continuing to provide heat to the boil-
er tank.
Troubleshoot the AC high-limit thermostat if the following
condition has occurred:
 The electric heating element fails to operate.
Troubleshooting:
1. Disconnect all power supplies.
2. Remove the thermostat access cover.
3. Verify that the boiler tank’s temperature is below 230°F.
4. Locate the AC high-limit thermostat and remove its
wires.
5. Using an ohmmeter, check the thermostat for continuity.
If continuity is not present, follow the instructions in this
section to replace the AC high-limit thermostat.
Replacement Procedure:
FAILURE TO DISCONNECT ALL POWER SUPPLIES AND/OR
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. Also, because this replacement procedure will in-
volve the boiler tank and the potential for hot coolant, be
sure the heater has adequately cooled.
2. Disconnect the defective thermostat’s wires by remov-
ing the screws securing the wires to the terminals.
3. Using a 1/4” nut driver, unscrew the two screws secur-
ing the thermostat to the Aqua-Hot’s boiler tank thermo-
stat mounting bracket.
4. Install the replacement thermostat into the thermostat
mounting bracket and secure with the two screws previ-
ously removed.
5. Inspect the wires going to the thermostat, Replace if
necessary. Re-Connect the thermostat’s wires and se-
cure in place using the screws previously removed.
6. Test the Aqua-Hot for normal operation.
Figure 10
Note: If a screw longer than 1/4” is used to secure the
thermostat in place, it may cause the thermostat mounting
bracket to be pushed away from the boiler tank, and may
result in overheating.

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© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
DC High-Limit Thermostat:
The DC high-limit thermostat 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
thermostat allow the current for the diesel-burner to pass
through it until the boiler tank reaches a temperature of
230°F. Should this temperature be reached, the high-limit
thermostat blocks the current to the diesel-burner’s fuel sole-
noid valve, which prevents the diesel-burner from operating.
Troubleshoot the DC high-limit thermostat if the following
condition has occurred:
 The fuel solenoid on the diesel-burner fails to operate.
Troubleshooting:
1. Place a jumper wire between the blue and purple wires
on the diesel-burner’s wire harness to bypass the high-
limit thermostats. Check the Aqua-Hot for normal oper-
ation.
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 DC high-limit thermostats’ wires, then,
using an ohmmeter, check the thermostat for continuity.
If there is no continuity, complete the following, follow
the instructions in this section to replace the high-limit
thermostat.
Replacement Procedure:
FAILURE TO DISCONNECT ALL POWER SUPLIES AND/OR 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 disconnected. Also,
because this replacement procedure will involve the boiler
tank and the potential for hot coolant, be sure the heater
has adequately cooled.
2. Disconnect the defective thermostat’s wires by separating
the quick-disconnect terminals.
3. Using a 1/4” nut driver, unscrew the two screws securing
the control thermostat to the Aqua-Hot’s boiler tank ther-
mostat mounting bracket.
4. Install the replacement thermostat into the thermostat
mounting bracket and secure with the two screws previ-
ously removed.
5. Inspect the quick connectors on the thermostat wires. Re-
place if necessary. Re-Connect the thermostat’s wires
(blue and purple).
6. Test the Aqua-Hot for normal operation.
Figure 11
Note: If a screw longer than 1/4” is used to secure the
thermostat in place, it may cause the thermostat mounting
bracket to be pushed away from the boiler tank, and may
result in overheating.
Note: If the control and overheat thermostat wires are
hooked up to the wrong thermostat, the diesel burner will de-
fault every time the heater reaches the maximum operating
temperature.

— Page 20 —
© 2011 Aqua-Hot® AHE-100-02S Hydronic Heating System Service Manual—Rev. B
SECTION 5: AQUA-HOT COMPONENTS
Valves
Check Valve:
Check valves are installed into the zone outlet ports for each
heating loop to ensure that the antifreeze and water heating
solution only flows in one direction. If the heating solution
attempts to backflow into the boiler tank, the check valve
closes to prevent that from happening.
Troubleshoot the check valves if the following condition has
occurred:
 There is a lack of interior heat in a particular zone.
Troubleshooting:
1. Verify that the heating zone is operating properly by
checking the following:
A. Verify that the room thermostat inside the interior
of the motor home is on and calling for heat.
B. Check the circulation pump for operation by feeling
the pump for a vibration, indicating the pump is
running.
2. With the circulation pump operating, tap on the check
valve and wait five minutes to evaluate if interior heat is
now present.
If interior heat is present after tapping the check valve,
the check valve was stuck closed and no further action is
necessary.
3. Check the Aqua-Hot’s antifreeze and water heating solu-
tion’s ratio of water to antifreeze. The mixture ratio
should be approximately 50/50. If the solution is com-
prised fully of antifreeze (100%), the check valves will
continue to stick.
NOTE: Storing the motor home for an extended period of
time can cause the check valves to stick. If, after the initial
release of the stuck check valve, it continues to stick, follow
the instructions in this section to replace the check valve.
Replacement Procedure:
FAILURE TO DISCONNECT ALL POWER SUPPLIES AND/OR
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. Also, because this replacement procedure will in-
volve the boiler tank and the potential for hot coolant, be
sure the heater has adequately cooled.
NOTE: Before Troubleshooting the zone check valve it is
important to remember that if the zone circulation pump is
air locked, or if there is a kink in a zone heating loop plumb-
ing line, the customer will experience the same symptoms as
a stuck check valve.
Figure 12