Aqua-Hot 400 series User manual

USE & CARE GUIDE
400SERIES
400-D

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Journey in Comfort
Thank you for equipping your RV with an Aqua-Hot hydronic heating system! We
value your business and are grateful for the trust you have placed with Aqua-Hot
Heating Systems Inc. Our customers are top priority and we are committed to
providing best-in-class products, service, and support.
We understand how important comfort is to you as a motor home owner; there-
fore, we have designed a heating system to significantly improve all of your com-
fort levels while on the road. Additionally, the Aqua-Hot hydronic heating system is
a low emission, fuel efficient system that adds thousands of dollars to your motor
home.
We know you must be eager to get underway, but take time to read the entire
Use & Care Guide and understand your Aqua-Hot unit. This guide should be main-
tained in legible condition and kept in a safe, accessible location for future review.
Should you have any suggestions how we can better serve you, please do not
hesitate to contact us at 800-685-4298 or 303-651-5500.
The Aqua-Hot hydronic heating system is protected by the finest warranty in the
industry (read it on page 19).
IMPORTANT NOTE:
 A qualified installer or service technician must perform equipment installation
or service. Contact Aqua-Hot for Factory Authorized Service Center or Certified
Technician located near you: www.aquahot.com / service-help: 800-685-4298
or 303-651-5500.
 Warranty work must be performed by and Aqua-Hot Factory Authorized Service
Center.
IMPORTANT NOTE:
 Your on-product identity label contains specifications of your unit. Factory set-
tings may have been adjusted by your RV manufacturer, confirm final setting
with your dealer.
WARNING:
 If the information in this book is not followed exactly, a fire or explosion may
result, causing property damage, or personal injury.

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Journey in Comfort
Comfort Zone #1: Comfortable Cabin Heat.
Get heat where you want it, when you want it! The Aqua-Hot system heats by zones. Therefore, your bedroom, living room, and
bathroom can be custom temperatures. Don’t hesitate to crank up the heat because the Aqua-Hot system doesn’t remove
moisture from the air. From now on, you will have to blame the dry skin and itchy eyes on Mother Nature!
Comfort Zone #2: Quiet Operation
Say goodbye to rude awakenings from the forced air furnace, you’re an Aqua-Hot owner now! The Aqua-Hot is quiet when op-
erating, so you’ll never have to turn up the TV, yell across the room, or have an interrupted night of sleep again due to your
heating system.
Comfort Zone #3: Continuous, On-Demand Hot Water
Take long, guilt free showers knowing there is no recovery time for the next shower or load of laundry. The freedom to take a
shower when you want makes your RV experience feel much more like home.
Comfort Zone #4: Low Emissions
Aqua-Hot’s new low emission systems are fumeless and odorless. It’s good for you,
good for your neighbor, and good for the environment.
Comfort Zone #5: Over 160 Factory-Trained Service Centers
You won’t need to service your Aqua-Hot often, but when you do, you can be confident in our Certified Service Centers that are
close by and trained to assist you with all of your Aqua-Hot specific needs.
Comfort Zone #6: Adds Value
The NADA Recreational Vehicle Guide lists Aqua-Hot as adding thousands of dollars to the value of an RV. That value will pay
off when it’s time to trade up or sell.
Comfort Zone #7: Low Fuel Costs
There’s no need to burn propane each time heat or hot water is needed. Aqua-Hot’s TribridHot technology powers the Aqua-
Hot system by pulling heat from one or a combination of heat sources. When shore power is available, simply plug it in. When
dry-camping or in very cold conditions, use the Diesel Burner.

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Contents Caution Notes
As you read this Information, take particular note
of the NOTICE, CAUTION, WARNING and
DANGER symbols when they appear. This infor-
mation is important for safe and efficient use of
the Aqua-Hot equipment.
NOTICE signals a situation where potential dam-
age to the equipment could occur.
CAUTION signals a situation where potential harm
or risk of minor or moderate injury could occur if
you do not follow instructions
WARNING signals a hazardous situation where
potential harm, risk of serious injury or death
could result if you do not follow instructions
DANGER signals a situation where immediate risk
of serious injury or death will result if you do not
follow instructions
NOTE: In addition, this manual may indicate an
IMPORTANT NOTE that highlights information that
is especially important.
Contents & Cautions
Safety Instructions & Precautions ---------------------------------------5
Aqua-Hot Heating System Features
400-D -------------------------------------------------------------------------------6
Cut-Away Diagrams----------------------------------------------------------- 7
Controls Overview
Switches -----------------------------------------------------------------------8
Thermostats -----------------------------------------------------------------8
Interior Heating Operation
Heating Operation-------------------------------------------------------------8
Controlling Heat Levels ----------------------------------------------------8
Control/Balancing Heating Zones -----------------------------------8
Hot Water Operation
Using the Water Heating System
General Information ----------------------------------------------------9
Operation Instructions------------------------------------------------ 9
Operational Flowchart ---------------------------------------------------------10
Care and Maintenance
Overview--------------------------------------------------------------------------11
Monthly----------------------------------------------------------------------------11
Annual -----------------------------------------------------------------------------11
Winterization -------------------------------------------------------------------11
Disinfecting the Domestic Water System----------------------11
Fluids
Types --------------------------------------------------------------------------12
Mixture Recommendations ---------------------------------------12
Mixture Ratios------------------------------------------------------------13
Using a Refractometer-----------------------------------------------14
Trouble Shooting Guide
General Information -------------------------------------------------------15
Electronic Diagnosis -------------------------------------------------15-16
Tempering Valve -------------------------------------------------------------16
Owner’s Service Log ------------------------------------------------------17-18
Aqua-Hot Warranty --------------------------------------------------------------19

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Safety Instructions & Precautions
The Unit
IMPORATANT NOTE: Read all instructions before using this
appliance.
 Read this Use & Care Guide before using your Aqua-Hot
Heating System to reduce the risk of injury to persons
or damage to equipment.
 Have your dealer show you the location and operation
of all switch operations and valve settings.
 Do not repair or service the system, unless specifically
recommended in the literature accompanying the Aqua-
Hot product. All service should be referred to a qualified
technician.
 An interlock switch prevents the Aqua-Hot heater from
operating when the cover is not installed in the correct
position.
 Propylene glycol based antifreeze, “Generally Recog-
nized as Safe” by the FDA, must be utilized for anti-
freeze and water heating solution.
 Interior heat can still be used once the water heating
system has been drained and winterized.
 Use propylene glycol “Generally Recognized as Safe” RV
and Marine antifreeze specifically for “winterizing” ap-
plication ONLY.
CAUTION:
 The hot water temperature is set at the mixing valve to
120°F/ 48.9°C at the factory.
 DO winterize the heating system when freezing temper-
atures are expected to avoid serious damage to the hot
water system.
 DO NOT operate the burner or electric heating element
without antifreeze or water heating solution in the boil-
er tank to avoid damage to the heater.
 Aqua-Hot’s exhaust is hot. DO NOT park in dry areas
when operating to avoid fire and injury to persons.
 At maximum operating temperatures, the coolant will
be very hot and scalding hot vapor or coolant may re-
sult in serious burns or injury.
 Before cleaning or servicing, disconnect all power sup-
plies.
 The heater must be switched OFF when refueling.
 DO NOT operate the Aqua-Hot’s diesel-burner inside an
enclosed building.

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Aqua-Hot Heating System Features
400-D Features
The Aqua-Hot Heating System is a Low Emissions Hy-
dronic Heating System (heating with hot water) that signifi-
cantly improves your level of comfort, decreases harmful
emissions released into the atmosphere, and adds thou-
sands of dollars to your RV.
The Aqua-Hot Heating System is three systems in one:
1. Interior Heating System: provides quiet, comfortable
interior heat with independent temperature zones that
provide cabin-wide, even temperatures.
2. Bay Heating System: keeps pipes and tanks from freez-
ing in the bay storage area.
3. Tank-less Hot Water System: provides a steady flow of
continuous hot water.
The Aqua-Hot System is powered by TribridHot™ technology
and uses one or a combination of the following sources:
1. The 120 Volt-AC Electric Element: When plugged into
shore power, the electric element lets you use the pow-
er you are already paying for to provide heat and meet
your light duty hot water needs.
2. The Diesel Burner: This is the Aqua-Hot’s most powerful
heat source and provides all of heating and hot water
needs in cold temperatures or dry camping.
NOTE: This Aqua-Hot product utilizes a propylene glycol
based antifreeze and water heating solution. This propylene
glycol based solution is a boiler type antifreeze that is
“Generally Recognized as Safe” (GRAS) by the FDA. For
additional information regarding this “GRAS” antifreeze
product, please reference the Care & Maintenance section
of this guide, contact the Aqua-Hot Heating Systems Tech-
nical Support Department at 1-800-685-4298, or visit the
web site at www.aquahot.com.
The product label
attached to the
Aqua-Hot
provides a ready
reference to
specifications, test
standards, and
important safety
notices.

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Cut-Away Diagrams
1. AC Terminal Block
2. AC Terminal Port
3. AC Wiring Port
4. Access Cover
5. Air Release Valve
6. Diesel Burner
7. Diesel Burner Controller
8. Diesel Fuel Inlet/Outlet Ports
9. Domestic Cold Water Inlet
10. Domestic Hot Water Outlet
11. Drain Valve
12. Expansion Tank Connection
13. Heating Zone 1 Outlet Port
14. Heating Zone 2 Outlet Port
15. Tempering Valve
16. VAC Access Panel
17. Wiring and Harness Port
18. Zone 1 Circulation Pump
19. Zone 1 Inlet Port
20. Zone 2 Circulation Pump
21. Zone 2 Inlet Port
Aqua-Hot Heating System Features
1
2
6
7
11
13 14
16
18 20
4
3 58
9
10
12
15
17
1921
NOTE: Service parts and accessories are available
through Aqua-Hot Factory Authorized Service Center or
at www.aquahot.com.

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Aqua-Hot Heating System Features
Controls Overview
Do not operate the diesel-burner and/or electric element
without the antifreeze and water heating solution in the
Aqua-Hot’s boiler tank. Failure to do so will cause serious
damage to the heater.
Switches:
The Aqua-Hot heating system is controlled by two switches,
the burner switch and the electric element switch. When
one or both of these switches are in the ON position, it will
supply the necessary heat to the boiler tank. Keep in mind
that the Aqua-Hot must be at operating temperature for the
heating zones and hot water to function properly. Please
contact the specific motor home dealer for exact location of
switch operations.
Thermostats:
The interior room thermostat can be set at the desired tem-
perature; therefore, whenever the interior of the room “calls
for heat”, the Aqua-Hot’s circulation pump and interior heat
exchanger fans will be activated. The fresh water thermostat
controls the bay heating area and should NOT be set below
40°F, to prevent freezing of the domestic water storage sys-
tem. Please contact the specific motor home dealer for exact
location of thermostat controls.
Interior Heating Operation
Heating Operation
Overview:
The heating features are powered by a 12 Volt-DC diesel-
burner and a 120 Volt-AC electric heating element. These
two heating elements maintain the temperature of the Aqua
-Hot’s antifreeze and water heating solution to provide hot
water and heat to the motorhome.
 Diesel–The diesel-burner is the Aqua-Hot’s primary and
most powerful heat source and provides all of the heat-
ing and hot water needs when cold temperatures exist
and/or when there is a high demand for hot water. It
can be activated by turning the burner switch in the ON
position. Reference Figure 1 on following page.
 Electric–The electric element is the Aqua-Hot’s second-
ary heat source and can be used when plugged into
shore power. The electric element provides heat when
moderate temperatures exist (50°F or higher) and/or
when there is a low demand for hot water. It can be
activated by turning the electric switch in the ON posi-
tion. Reference Figure 1 on following page.
Controlling Heat Levels:
The interior room thermostat can be adjusted at the de-
sired temperature and will automatically be activated to
maintain the temperature of the interior. Keep in mind that
the diesel and/or electric element switch must be in the ON
position for the heat to operate.
Control/Balancing Heating Zones:
Set the interior room thermostat for each independent
heating zone at the desired temperature. This feature al-
lows you to customize various temperatures on each heat-
ing zone throughout your motor home.

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Interior Heating Operation
Using the Water Heating System
General Information:
The Aqua-Hot system is known as an on-demand hot
water heating system because hot water is not stored with-
in the motor home. Instead, when the burner and/or elec-
tric element switch is ON and the Aqua-Hot is at operating
temperature, the water is automatically heated as it is be-
ing used. Therefore, simply open an hot water faucet once
system is up to operating temperature, and a continuous
supply of hot water will be present within a few seconds.
Do not operate the diesel-burner and/or electric element
without the antifreeze and water heating solution in the
Aqua-Hot’s boiler tank. Failure to do so will cause serious
damage to the heater.
The Aqua-Hot’s exhaust is HOT! Do NOT park is areas
where dry conditions exist (i.e., grassy, dry fields). Do NOT
operate the diesel-burner inside an enclosed building. The
heater must be switched OFF when refueling.
Operation Instructions:
To operate the Aqua-Hot hot water system, you will need
to locate the interior switch panel located inside your mo-
torhome. If you are unable to locate the switch panel, con-
tact your dealer to guide you in the location and operation
of all switch operations. Once you have located the interior
switch panel, turn the burner switch ON. This action will acti-
vate the diesel-burner and the indicator light located adja-
cent to the diesel-burner switch. Allow 10-20 minutes for
the Aqua-Hot system to reach operating temperature.
Please note that the diesel-burner is the primary heat
source for heating the interior and hot water.
To operate the electric heating element, turn the electric
switch ON. This action will activate the 12 Volt-AC electric
heating element and the indicator light located adjacent to
the electric switch. Allow 1-2 hours for the Aqua-Hot system
to reach operating temperature. Be sure to activate the
electric element switch for maximum water capacity. Figure
1 is an example of an interior switch panel.
NOTE: The switch panel in your RV may look like either of
the switch panels represented by Figure 1. The Aqua-Hot
400 does not have the Engine Preheat function, so if the
three switch panel is present, the Engine Preheat switch
will be inactive.
Figure 1

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Electric Heating Element is
activated by the Electric
switch.
Heat source is selected from the Interior
Switch Panel.
Diesel-Burner is activated
by the Burner switch.
The cooled antifreeze and water
heating solution is returned to the
boiler tank to be reheated.
Heating Zone Thermostat
calls for heat.
The heated antifreeze and
water heating solution flows
through the Hydronic Heat-
ing System transferring
heat to the heat exchanger,
which is then transferred to
the surrounding zone.
A hot water faucet (e.g., kitchen
sink, shower, etc.) is opened.
Continuous hot water is supplied
to the faucet.
The Boiler Tank heats the
antifreeze and water heat-
ing solution to 190°F.
Operational Flowchart

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Care & Maintenance
Overview:
The Aqua-Hot system requires minimal maintenance if
monthly, annual, and proper winterization procedures are
followed accurately. It is extremely important to follow the
instructions below precisely and carefully to receive the best
results and promote the longevity of your Aqua-Hot. Monthly
maintenance to the Aqua-Hot requires a visual check of the
antifreeze and water solution to make sure it’s at the cor-
rect operating level. Annual maintenance to the Aqua-Hot
requires a replacement of two parts on the diesel-burner,
the fuel nozzle and fuel filter. Winterization of an Aqua-Hot
system prepares a motor home for storage during the winter
months to prevent freezing pipes and other critical damage.
When the Aqua-Hot is at maximum operating temperature,
the coolant will be very HOT! If the Aqua-Hot’s heating sys-
tem is accessed, scalding hot vapor or coolant could result.
Before cleaning or servicing, disconnect all power supplies.
Monthly:
It is extremely important to check the Aqua-Hot’s anti-
freeze and water heating solution to ensure it is at the prop-
er level for operation. This task can be done by visibly
checking the coolant level in the Aqua-Hot’s expansion tank.
At maximum operating temperature, the antifreeze and wa-
ter heating solution should be at the level marked “HOT” on
the expansion tank. The coolant level should be checked
ONLY when the Aqua-Hot is at maximum operating tempera-
ture. Therefore, this procedure should be done immediately
after the diesel-burner cycles OFF. Reference figure below. If
it needs refilling, reference “Fluids” in the Care & Mainte-
nance section.
Annual :
In order to keep the Aqua-Hot running at its full potential, it’s
highly recommended to have the diesel-burner tuned up an-
nually. This tune up consists of a new fuel nozzle and fuel
filter. To ensure maximum diesel-burner performance, always
use the recommended fuel nozzle and fuel filter when replac-
ing these parts. Reference the Aqua-Hot’s Service and Parts
Manual for spare parts information and detailed replacement
attachments.
Winterization:
When it’s time to store a motor home for the winter
months or when freezing temperatures are expected, it’s cru-
cial to properly winterize the Aqua-Hot to avoid serious dam-
age, requiring a complete system replacement not covered
under the Aqua-Hot Limited Warranty Statement. The process
of winterization consists of completely draining the domestic
water from the system and pumping RV winterization anti-
freeze through to flush out the system.
Not winterizing the Aqua-Hot when freezing temperatures are
present will result in SERIOUS damage to the Aqua-Hot’s Do-
mestic Water Heating System. Also, be sure to use the FDA
approved, “GRAS” rated antifreeze for winterization.
Please follow these instructions carefully when winterizing the
Aqua-Hot’s hot water heating system:
1. Completely drain the fresh water storage tank.
2. Disconnect the domestic water demand pump’s suction
line from the fresh water storage tank.
3. Attach an adequate piece of hose onto the suction side of
the domestic water pump.
4. Place the opposite end of the hose into an adequate sup-
ply of the RV antifreeze, “GRAS” by the FDA and allow this
to pump through the system.
5. Open and close all interior and exterior water faucets,
one at a time. Until ONLY pure RV antifreeze is present.
Perform this procedure for both hot and cold faucets.
6. Remove the hose from the RV antifreeze and reconnect
the domestic water demand pump’s suction line to the
fresh water storage tank.
Expansion Tank
Cap
Fluid will reach
Expansion
Tank line when
HOT

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De-Winterization:
To de-winterize the Aqua-Hot system, completely fill the
fresh water storage tank. Open and close the interior and
exterior faucets, one at a time, until only clear water is pre-
sent.
Disinfecting the Water System:
Aqua-Hot systems contain copper tubing and are not com-
patible to prolonged exposure to sodium hypochlorite
(bleach or liquid bleach). Using products containing bleach,
including water refreshers, may cause corrosion of the
domestic water coil, resulting in a catastrophic failure of
the Aqua-Hot system by creating leaks that cannot be
repaired. This damage is not covered by the Aqua-Hot war-
ranty.
If disinfecting the hot water heating system be sure to follow
NFPA 1192 Standard on Recreational Vehicles’
“Instructions for Disinfection of Potable Water Systems.”
These instructions can be found by visiting the National Fire
Protection Association online at www.nfpa.org.
Fluids:
Overview:
When the antifreeze and water heating solution needs
replenishing, remove the expansion tank’s cap and fill to the
“HOT” level mark. When refilling, open the air release valve
located on the expansion tank connection to release air
pockets. Be sure the valve is closed when finished by hand
tightening.
Care & Maintenance
Types:
Due to the significant impact of various types of anti-
freeze on the Aqua-Hot system, it is necessary to provide a
thorough explanation regarding what should and should not
be used. It’s very important use the correct type of anti-
freeze for adequate operation and condition of the Aqua-Hot
System. The necessary type of antifreeze is propylene glycol
based “boiler” type deemed “Generally Recognized as Safe”
by the FDA. Propylene glycol is a safer alternative to the
more toxic ethylene glycol antifreeze.
RV and Marine antifreeze types are propylene glycol
based, but formulated specifically for “winterizing” applica-
tion ONLY. Although RV and Marine antifreeze is often
“Generally Recognized as Safe” by the FDA, it should never
be used in the Aqua-Hot System because it’s not formulated
to transfer heat, which is absolutely essential for the func-
tionality of the Aqua-Hot.
Automotive Antifreeze/Coolant types of antifreeze are
propylene glycol based and formulated specifically to pro-
tect the automotive engines against, corrosion, freezing
temperatures, and overheating. In addition, they have excel-
lent heat transfer and thermal conductivity characteristics.
Although these types of antifreeze are considered less toxic
and safer than ethylene glycol, they are not “Generally Rec-
ognized as Safe” by the FDA. Therefore, they must be
marked with “harmful if swallowed” warning label. Due to
the potentially hazardous properties, Automotive Antifreeze/
Coolant should NEVER be used in an Aqua-Hot System.
Mixture Recommendations:
To ensure maximum performance and longevity of the
Aqua-Hot system, it has been determined to use distilled, de
-ionized, or soft water in commination with concentrated
propylene glycol for the antifreeze and water heating solu-
tion. Concentrated propylene glycol should be diluted with
high-quality (distilled, diluted, or soft) water, which is 80
ppm or less in total hardness. In order to find this infor-
mation, the local water agency should have up-to-date water
quality reports, which will indicate is the local tap water
meets the requirements.
Hard water possesses a high-level of calcium and mag-
nesium ions, which deplete the propylene glycol antifreeze’s
corrosion inhibitors. This causes the antifreeze and water
heating solution to turn acidic, which can corrode the Aqua-
Hot’s boiler tank and associated components prematurely.
Keep in mind that using high-quality water is only necessary
for mixing concentrated propylene glycol antifreeze with

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water. Suppliers of premixed antifreeze are responsible to
use distilled, de-ionized, or soft water when preparing their
antifreeze, so consumers shouldn't have to worry about it.
Mixture Ratios:
Technical Information:
Propylene glycol based (PPG) antifreeze has three major
functions including freeze, boiling, and rust/anti-corrosive
protection. PPG antifreeze solution is also primarily respon-
sible for heat transfer; however, propylene glycol itself does
not posses acceptable heat transfer characteristics. There-
fore, water is added to the mixture because it is an excel-
lent heat conductor. PPG antifreeze solution, mixed with
water that is 30-50% propylene glycol is recommended to
provide the best performance combination. If the antifreeze
and water heating solution contains over 70% propylene
glycol, the freezing point is actually increase, resulting in
less freeze protection. A perfect 50/50 mixture of water to
propylene glycol, “GRAS” by the FDA antifreeze is recom-
mended, which will result in a freeze point of –28°F and a
boiling point of approximately 222°F. Please reference the
graphical representation regarding the percentage of anti-
freeze to water and how it directly affects the solution’s
freezing point.
Freeze and Burst Point:
Antifreeze solution lowers the freezing point of any liquid to
Care & Maintenance
which it has been added by preventing the formation of
crystals. However, as ambient temperature continues to
decline, the water in the solution will attempt to attain a
solid state. The point at which the water begins to solidify
is called the “freeze point”. Although the water solution has
begun to freeze, producing a “slushy” consistency, the anti-
freeze in the solution will continue to combat normal ex-
pansion of the solution as it freezes. The point in which the
solution can begin to expand, due to colder temperatures,
is called the “burst point”. Once the solution reaches the
burst point, the potential is present for ruptured pipes and
other components. The burst point of the antifreeze and
the water heating solution is dependent upon the brand of
propylene glycol antifreeze employed.
Boiling Point:
The Aqua-Hot utilizes the propylene glycol based (PPG)
antifreeze and water heating solution as a transportation
means for the heat produced from the internal processes.
The PPG antifreeze solution absorbs the heat created until
its boiling point is reached. At this point, the liquid turns to
gas and is expelled to prevent the heating system from
overheating. Each time the boiling point is reached, a loss
of efficiency occurs because the heat produced is expelled
rather that utilized for the function of the heating system.
Therefore, a higher boiling point is desired in order to com-
bat the loss of efficiency, which
allows the antifreeze to transport
the heat created from the internal
process throughout the mo-
torhome where it can be utilized
productively rather than dissipat-
ing due to its change from a liquid
to a gas.
Rust and Anti-Corrosive Inhibitors:
Another major function of anti-
freeze solution is to provide protec-
tion to the internal metal compo-
nents of the Aqua-Hot hydronic
heating system for corrosion and
rust. Antifreeze is able to preform
this function by addition of rust
and anti-corrosive inhibitors, which
are designed specifically to acti-
vate in a water solution.

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Care & Maintenance
Using the Refractometer to Test Antifreeze Sample
Use extreme caution in gathering your antifreeze sample.
When draining the Aqua-Hot heating system, extremely hot
liquid may be in the boiler tank and could cause personal
injury.
Basic Operation
Step 1:
Open daylight plate, and place 2 to 3
drops of the sample on the main
prism. Close the daylight plate so the
liquid sample spreads across the en-
tire surface of the prism without air
bubble or dry spots. Allow the sample
to rest on the prism for approximately
30 seconds before going to step 2.
(This allows the sample to adjust to
the ambient temperature of the refrac-
tometer).
Step 2:
Hold daylight plate in the direction of a light
source and look into the eye piece. You will
see a circular field with graduations down
the center (you may have to focus the eye-
piece to clearly see the graduations). The
upper portion of the field should be blue,
while the lower portion should be white.
Step 3:
Take the reading where the boundary
line of the blue and white cross the
graduate scale. The scale will provide a
reading of the freezing point of anti-
freeze solution and the propylene gly-
col concentration. Clean the prism
carefully using a damp soft cloth. Do
NOT immerse in water.
Eyepiece
Calibration Screw
Daylight Plate
Assembly
Main Prism
Assembly
Aqua-Hot Part Number MSX-907-162
NOTE: Refractometers may have more than one
scale. Make sure you are reading the scale
marked “Propylene” for measuring the antifreeze
solution in the Aqua-Hot System.

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Troubleshooting Guide
Should the Aqua-Hot Hydronic Heating System fail to
operate, complete the following checks:
1. Verify that the Aqua-Hot’s access cover is securely in-
stalled. Reference page 7 (part #4). The Aqua-Hot Hy-
dronic Heating System will not operate if the access
cover is not fully installed.
2. Ensure that the vehicle’s fuel tank contains a sufficient
level of fuel. The Aqua-Hot system will not operate if
the fuel level is at or below 1/4 tank.
3. Ensure that the Aqua-Hot’s boiler tank has an ade-
quate supply of antifreeze and water heating solution
by checking the level at the Expansion Tank. If the level
is low, reference the Care & Maintenance section of
this guide for refilling instructions.
4. Check the Aqua-Hot’s electronic controller for any RED
lights indicating a fault condition.
If the Aqua-Hot Heating System’s failure to operate is
not resolved with the aforementioned checks, please con-
tact the Aqua-Hot Heating Systems Technical Support De-
partment at 1-800-685-4298 for additional assistance or
visit the web site at www.aquahot.com.
If the Aqua-Hot’s diesel-burner switch “Indicator Light”
does not illuminate and the diesel-burner is not functioning,
locate the electronic controller and check the following:
1. Check the Aqua-Hot’s electronic controller for any RED
lights indicating a fault condition. Reference Figure 2.
2. Check for loose wire connections on the electric con-
troller’s terminal strips/plugs. When checking for loose
terminal strips/plugs, remove the electronic controller
faceplate by unscrewing the four cover screws.
3. Remove the Aqua-Hot’s access cover and check for
loose plug connections on the diesel-burner controller
unit. Reference page 7 (part #4).
4. Ensure the vehicle’s fuel tank has a sufficient level of
fuel.
5. If the Aqua-Hot still fails to operate, please contact the
Aqua-Hot Heating Systems Technical Support Depart-
ment at 1-800-685-4298 or visit the web site at
www.aquahot.com.
NOTE: An interlock switch prevents the Aqua-Hot from op-
erating when the cover is not installed and properly in
place.
General Information Electronic Controller Diagnosis
Low Tank-Level Cutoff Indicator Light:
This indicator light will illuminate RED when either the
120 Volt-AC electric heating element and/or diesel-burner
have automatically shut down due to low antifreeze and
water heating solution level inside the Aqua-Hot’s boiler
tank. This fault will automatically reset when the low level
condition is corrected.
Low Battery Voltage Fault Indicator Light:
This indicator light will illuminate RED and the Diesel-
Burner will shut down whenever the 12 Volt-DC voltage level
is too low for the Aqua-Hot to operate properly. This fault
must be manually reset after the voltage level has been
restored to the 12 Volt-DC battery system. Reference “Low
Voltage Fault Indicator Light and Reset Button” information
below.
Low Voltage Fault Indicator Light and Reset Button:
The Aqua-Hot’s electronic controller must be manually
reset whenever the low battery voltage fault indicator light
has been activated.
The electric controller can be reset by turning OFF the
diesel-burner switch on the interior switch panel for approxi-
mately 60 seconds, then turning the switch back ON by
pressing the “Low Voltage Reset” button located on the
electric controller (use a thin, straight, non-metallic object to
access the reset button through the small hole on the face-
plate).
Overload Fault Indicator Light:
This indicator light will illuminate RED whenever one of
the following conditions have occurred:
1. The Aqua-Hot is off due to an electrical overload (i.e.,
short) in the main 12 Volt-DC power supply circuitry.
2. The Aqua-Hot is off due to a combination of high electri-
cal 12 Volt-DC power loads and a high surface tempera-
ture of the electronic controller.
The Aqua-Hot will automatically restart once the elec-
toral overload (i.e., short) and/or high-heat condition is cor-
rected.

Secon #: Title
© Aqua-Hot® 400-D Use & Care Guide 16
p.
Troubleshooting Guide
Troubleshooting
Heating Zones Status Indicator Lights:
These five indicator lights (separately) will illuminate
GREEN whenever a zone thermostat, for each particular
zone, is calling for heat. The GREEN indicator lights also
indicate that 12 Volt-DC power is being supplied to the par-
ticular interior heating zone’s heat exchangers (i.e., fan
motors).
If any of the five indicator lights illuminate RED, it indicates
that an electrical overload condition (i.e., short) has oc-
curred in a particular heating zone's circuitry.
Pumps #1, #2, and #3 Indicator Lights:
These indicator lights (separately) will illuminate GREEN
whenever a circulation pump is operating. If any of the
three indicator lights illuminate RED, it indicates that an
electrical overload condition (i.e., short) has occurred in the
particular component’s circuitry.
Electric Heating Element Status Indicator Light:
This indicator light will illuminate GREEN whenever the
Aqua-Hot’s electric heating element is operating and
providing heat to the Aqua-Hot’s boiler tank.
Please note that this light will only be active if the elec-
tric element switch is ON. If this indicator light illuminates
RED, it indicates an electrical overload condition (i.e., short)
has occurred in the electric heating element’s 12 Volt-DC.
NOTE: Zone circulation pumps #1 and #2 are activated
whenever a zone thermostat “calls for heat”. The #3 boiler
tank stir pump is activated whenever the domestic water is
being used on a continuous basis or the heater is not up to
operating temperature.
NOTE: The Low Temp Cutoff Light must be illuminated and
the heater must be up to operating temperature for the
heating zone status indicator lights to illuminate red or
green.
NOTE: The Aqua-Hot’s VDC/VAC Control Thermostat will
automatically activate the Diesel-Burner and/or the electric
heating element ONLY if the Diesel-Burner and/or electric
element switch is in the ON position.
Figure 2
Tempering Valve
The Tempering Valve for the Aqua-Hot mixes the heated
domestic water from the boiler tank with cold domestic wa-
ter at the present ratio to reduce the risk of scalding. This
valve is located in the back of the Aqua-Hot unit. Reference
page 7 (part #15).
Locate the pink paint witness mark to verify that the Aq-
ua-Hot is set at the correct factory setting and did not get
tampered with during shipping or installation.
Verify that the Tempering Valve is set at the proper tem-
perature by using a digital thermometer at one of the hot
water faucets. The water temperature should range be-
tween 115°F to 123°F. If the correct temperature cannot be
set, please contact Aqua-Hot Heating Systems Technical
Support Department at 1-800-685-4298 for additional as-
sistance or visit the web site at www.aquahot.com.

Secon #: Title
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p.
DATE SERVICE PERFORMED SERVICE CENTER
Owner’s Service Log

Secon #: Title
© Aqua-Hot® 400-D Use & Care Guide 18
p.
DATE SERVICE PERFORMED SERVICE CENTER
Owner’s Service Log

© Aqua-Hot® 400-D Use & Care Guide 19
2-YEAR LIMITED WARRANTY AQUA-HOT®
HYDRONIC HEATING SYSTEM
Aqua-Hot Heating Systems Inc. warrants the Aqua-Hot Heater to be free from defects in material
and workmanship under normal use and service for a period of two years on both parts and
labor commencing upon the original date of registration of the vehicle. Replacement parts are
warranted for the remainder of the Heater’s standard warranty coverage or for six months,
whichever is greater. The intent of this warranty is to protect the Heater’s end-user from such
defects, which would occur in the manufacturing of the product. Thus, problems due to
improper specifications, improper installations, improper use, the use of accessory parts or
parts not authorized by Aqua-Hot Heating Systems Inc., repair by unauthorized persons, and
damage or abuse of the Heater are specially excluded from warranty coverage.
For additional information or to obtain a warranty repair authorization, please contact the
Aqua-Hot Heating Systems Warranty Administrator at 1-800-685-4298 (8:00 AM to 5:00 PM
Mountain Standard Time) or visit www.aquahot.com.
My Comfort Zones are On-Board
Vehicle:
Purchased From:
Dealer Information:
Name:
Location:
Phone Number:
Heating System:
Serial Number:
Warranty

7501 Miller Drive, Frederick, CO 80504
Visit us on line at www.aquahot.com
Call us at 1(800) 685-4298 or [phone]
©2013 Aqua-Hot Heating Systems Inc. Printed In U.S.A.
LTE-907-607 Rev. B