Aqua-Hot 200 Series User manual

Service Manual
200Series
AHE-250-P01

Introduction
©Aqua-Hot® 250 Series Propane Service Manual
p. 2
Caution Notes
As you read this information, take particular note of the NOTICE,
CAUTION, WARNING, and DANGER symbols when they appear.
This information is important for safe and effi cient use of the
Aqua-Hot system.
NOTICE signals a situation where potential damage to the
Aqua-Hot 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 instructions are
not followed.
DANGER signals a situation where immediate risk of serious
injury or death will result if instructions are not followed.
NOTE: This manual will also use notes sections similar to
this one to draw attention to features and practices which
must be observed.
Contents
Caution Notes ...............................................................................2
Introduction ..................................................................................3
Maintenance Schedule ................................................................6
System Features ..........................................................................7
Component Cut-Away ...................................................................8
Operational Flowchart..................................................................9
Relay Control Board ...................................................................10
Interior Switch Panel ................................................................. 12
Exhaust System Requirements ................................................ 13
Interlock Switch ..........................................................................14
Fluid Level Sensor ......................................................................15
Control Thermostat ....................................................................17
AC High-Limit Thermostat ..........................................................19
Burner High-Limit Thermostats .................................................21
Low-Temperature Cutoff Thermostat........................................22
Three-Way Valve .........................................................................24
Tempering Valve ........................................................................ 26
Fluid Circulation and Stir Pump ................................................27
AC Electric System..................................................................... 29
Propane Burner ................................................................ 31
Propane Burner Flow Chart ...................................................... 32
Propane Switch Panel ............................................................... 33
Fenwal Control Card .................................................................. 34
System Schematic .................................................................... 35
Detaching the Propane Burner ................................................ 36
Reinstalling the Propane Burner .............................................. 38
Mounting Gasket ....................................................................... 40
Hot Surface Igniter .....................................................................41
Refractory Insulation ................................................................. 43
Dual-Stage Propane Gas Valve ................................................. 44
Propane Combustion Blower Fan ............................................. 46
Adjustment of the Propane Air Shutter.....................................47
Exhaust “High Back” Pressure Switch......................................48
Fan Validation Switch ................................................................ 49
Buck Boost Converter - Combustion Blower Fan......................50
Buck Boost Converter - Hot Surface Igniter..............................51
Propane Flame Sensor ............................................................. 53
Fill and Purge Procedure .......................................................... 55
Winterization.............................................................................. 56
General Troubleshooting............................................................57
Burner Troubleshooting ............................................................ 59
Antifreeze Information .............................................................. 60
Appendix: Measuring Antifreeze .............................................. 62

Introduction
©Aqua-Hot® 250 Series Propane Service Manual p. 3
System Overview
The Aqua-Hot 250 Propane Series is a Hydronic (water-
based) Heating Systems that can provide heat and tank-less,
continuous hot water in one small, easy to install package.
The Aqua-Hot Heating is a 2-in-1 System
1. Interior heating system: provides moist, quiet, comfortable
interior heat and even temperatures. It is equipped with
one thermostatically-controlled temperature zone.
2. Tank-less hot water system: provides a fl ow of continuous
hot water. It produces 90 gallons per hour (1.5 GPM).
The system uses one or a combination of heat sources to
heat FDA-approved “Generally Recognized As Safe” (GRAS)
propylene glycol based antifreeze solution contained within
the Aqua-Hot boiler tank.
The 250P uses a 12-volt DC powered propane burner as
the primary heating source. The propane burner should be
used as the primary heating source for hot water and interior
heating needs. The 250P also has one 120-Volt AC 1000-Watt
electric element for use (when shore power is available) as a
heating source. Once the tank has been brought
to operating temperature by the propane burner, the electric
element can be used to maintain this temperature, as well as
provide hot water and interior heat for light-duty applications.
The burner and the electric element can be used together or
separately.
For continuous hot water or heat in colder conditions, it
is recommended to utilize the propane burner. The electric
heating element will provide heat only in mild conditions and
provide light duty hot water needs.
Should additional assistance be needed, please contact the
Technical Support at 574-AIR-XCEL (574-247-9235), Monday
through Friday, between 7:00am and 4:00pm MST.
Introduction to this Document
Welcome to the Aqua-Hot 250P Service Manual. This manual
will serve as a guide for diagnosing and repairing the Aqua-Hot,
how to perform standard maintenance, and guide you through
troubleshooting procedures to repair the Aqua-Hot. This service
manual is designed to aid trained and qualifi ed technicians to
properly service and troubleshoot the Aqua-Hot.
Each section in this manual is dedicated to the diagnosis
of specifi c components within the Aqua-Hot which may be
inhibiting the operation of the heater.
If additional assistance is needed in diagnosing and
repairing the Aqua-Hot, please contact our Technical Service
Department at 574-AIR-XCEL (574-247-9235) from 7:00am to
4:00pm MST Monday through Friday.
As with any appliance, allow the Aqua-Hot to
completely shut down BEFORE disengaging the
coach 12V power disconnect.
If the information in this manual is not followed
exactly, a fi re may result, causing property damage,
personal injury or death.
Figure 1

Introduction
©Aqua-Hot® 250 Series Propane Service Manual
p. 4
WHAT TO DO IF YOU SMELL GAS
• Evacuate all persons from the vehicle.
• Shut off the gas supply as the gas container or source.
• Do not touch any electrical switch or use any phone or radio
in the vehicle.
• Do not start the engine or electric generator (if equipped).
• Contact the nearest gas supplier or qualifi ed service
technician for repairs.
• If you cannot contact the nearest gas supplier or qualifi ed
service technician, contact the nearest fi re department.
• Do not turn on the gas supply until the gas leak or leaks (if
relevant) have been repaired.
• Installation and service must be performed by a qualifi ed
installer, service agency, or gas supplier.
The Aqua-Hot’s exhaust is HOT!
• Do NOT park in areas where dry conditions exist (IE grassy,
dry fi elds).
• Do NOT operate the burner inside an enclosed building.
• The heater must be switched OFF when refueling.
Read all instructions before servicing the Aqua-Hot unit. Aqua-
Hot Heating Systems is not liable for damage resulting from
failing to follow instructions contained in this, and any other
Aqua-Hot documentation relevant to this unit.
• Read this manual before installing or using the Aqua-Hot
System to reduce the risk of injury to persons or damage to
the equipment.
• The product identity label contains specifi cations of the
unit, to what standards it has been tested, and important
safety notices.
• The Aqua-Hot must be installed in a compartment that is
closed off from living quarters and accessible only from the
exterior of the vehicle.
• Propylene glycol based antifreeze “Generally Recognized
As Safe” (GRAS) by the FDA must be utilized for the
antifreeze and water heating solution.
• An interlock switch prevents the Aqua-Hot heater from
operating when the cover is not installed in the correct
position.
• Disconnect electric wiring to the Aqua-Hot System before
welding or plasma cutting the coach to avoid damage to
equipment.
• The Aqua-Hot tank and heating loop operate at 0.0 PSI
(zero pressure system). Air pressure to the tank must not
exceed 20 PSI. Exceeding this rating will cause internal
damage to the Aqua-Hot.
• Use caution when working on or near any propane/diesel
fuel system.
• Do not store or use gasoline or other fl ammable vapors or
liquids in the vicinity of this or any other appliance.
• The Aqua-Hot’s exhaust is HOT and must be kept away from
heat sensitive material.
• DO NOT connect the 12-volt DC power to the Aqua-Hot if the
vehicle requires welding.
• At maximum operating temperature, the coolant will be
very hot and scalding. Hot vapor or coolant may cause in
serious burns or injury. Be aware of hot surfaces.
• Do NOT activate the burner until the antifreeze and water
heating solution has been added to the boiler tank to avoid
serious damage to the heater.
• Installation and repairs may only be carried out by an
authorized, factory-trained Aqua-Hot technician. The
heating system must be installed in accordance with local
codes, or in accordance with the Standard for Recreational
Vehicles, (RVIA) ANSI A 119.2/NFPA 501C, NFPA 1192.
If the information in this manual is not followed exactly,
a fi re or explosion may result, causing property damage,
personal injury or death.
NOTE: Should any additional assistance be needed, please
contact the Technical Support Department at 574-AIR-XCEL
(574-247-9235).

Introduction
©Aqua-Hot® 250 Series Propane Service Manual p. 5

Introduction
©Aqua-Hot® 250 Series Propane Service Manual
p. 6
Maintenance Schedule
Maintenance Schedule
Monthly Maintenance
Check the Aqua-Hot’s antifreeze and distilled water heating
solution to ensure that it is at the proper level. This can be
accomplished by visually checking the coolant level in the Aqua-
Hot’s expansion bottle; reference Figure 10 on page 15.
Please note that the coolant level should be checked ONLY
when the Aqua-Hot is at maximum operating temperature.
This should be done immediately after the electric element
disengages, or after the propane burner has completed a cycle.
At maximum operating temperature, the antifreeze and distilled
water heating solution should be at the level marked “HOT” on
the expansion bottle.
It is also recommended to run the propane burner once a
month for a full cycle (at least 20 minutes) to ensure optimum
heater condition.
Annual Maintenance
The Aqua-Hot 250P has an extremely simple annual service
procedure. Remove the fl ame sensor and clean with a light
abrasive pad like a Scotch-Brite pad.
Replenishing the Antifreeze and Water Heating
Solution
If the antifreeze and distilled water heating solution needs
replenishing, remove the cap for the expansion bottle and fi ll
it to the “HOT” mark (only when the tank is to temperature).
Replace the expansion bottle cap when this is complete. DO
NOT operate the unit without fi rst replacing the cap of the
bottle. Reference Figure 10 for additional information. Excess
air will escape through this bottle as the stir pump of the unit
operates. While bleeding this system of air, it will be necessary
to continue to fi ll the bottle until this process is complete.
The Aqua-Hot does not need regular replacement of the
propylene glycol antifreeze and distilled water heating solution,
but in the event that more antifreeze is required, contact Aqua-
Hot Heating Systems to purchase antifreeze, or for guidance
in selecting an appropriate antifreeze product for use with this
unit.
When the Aqua-Hot is at maximum operating temperature, the
coolant is very hot. If the Aqua-Hot heating system is accessed,
scalding by hot vapor or coolant may occur. Before cleaning or
servicing, disconnect all power supplies.
DO NOT operate the propane burner and/or electric heating
element without antifreeze and distilled water heating
solution present in the Aqua-Hot’s boiler tank. Doing so will
cause serious damage to the heater.
Overheat Protection
Every Aqua-Hot is equipped with at least two overheat
protection devices. These are commonly known as the high-
limit thermostats. These thermostats operate by maintaining a
circuit while the unit is below 218°F (103° C).
In the event of an overheat condition, the high limit
thermostats will cut the operating signal to the propane burner,
and/or the electric element. When this signal is interrupted,
the electric element and propane burner will immediately
disengage. Contact Aqua-Hot Heating Systems LLC for
assistance in locating a qualifi ed person to service this heater
after an overheat situation.
In order to provide the best freeze protection, boil-over
protection, anti-corrosion, and rust protection, a mixture
of 50/50 propylene glycol antifreeze and distilled water
is recommended. The Aqua-Hot 250P boiler tank holds
approximately 3.7 gallons.
The mixture may be modifi ed to provide the most adequate
freezing, boiling, and rust/anti-corrosive protection. A 50/50
mixture of propylene glycol and distilled water has a freeze
point of approximately -35°F (-37°C) and a boiling point of
approximately 223°F (106°C). Refer to the table below to
determine the best protection mixture ratio. Reference page 62
for measuring the antifreeze mixture with a refractometer.
DO NOT attempt to reset the high-limit thermostats after
an overheat condition until the unit has been serviced by a
qualifi ed technician. Failure to do so could result in damage
to the unit, personal injury, or death.
Freeze
Point (°C)
Concentra-
tion (%)
0 -4 -7 -9 -12 -15 -18 -23 -29 -34 -40 -46
0 12 19 25 30 34 38 44 49 53 57 60
Propylene Glycol

Basic Components
©Aqua-Hot® 250 Series Propane Service Manual p. 7
System Features
System Specifi cations
Electric Element
Power Consumption ......................................1000 W (maximum)
Voltage ..............................................................................120V AC
DC Power
Heat Input ..................................................60,000 BTU/hr ± 10%
Fuel Consumption ..................................................0.66 gallon/hr
Power Consumption ........................................... 42W (maximum)
Zone Heat Circulation
Pumps ...........................................................................................1
Power Consumption (max) ..................................................... 21W
Voltage ............................................................................... 12V DC
Heating Zones
Maximum ......................................................................................1
Domestic Water Heating
Maximum ......................................................................... 1.5 GPM
Physical Specifi cations
Dimensions.....................................17.2”H x 12.46”W x 22.44”L
Dimensions (250PN)....................13.28”H x 16.54”W x 21.81”L
Dry Weight ........................................................................... 84lbs.
Wet Weight ......................................................................... 104lbs.
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.
Figure 2
NOTE: This product label is attached to the side of the
Aqua-Hot, and provides a ready reference to specifi cations,
test standards, and important safety notices.

Operational Flowchart
©Aqua-Hot® 250 Series Propane Service Manual
p. 8
NOTE: The side and top panels in the view below have been
made transparent to aid in the explanation of the heater. DO
NOT remove these panels. Doing so risks irreparable damage
to the Aqua-Hot. Only remove the service panel for service.
7810 11 13
5
4
3
2
1
15
16
6
17
18
9
1. Access Cover Screw
2. Drain Valve
3. Propane Burner Controller
4. Tempering Valve
5. 3-Way Valve
6. Propane Burner Assembly
7. Domestic Cold Water Inlet
8. Domestic Hot Water Outlet
9. Propane Inlet Ball Valve
10. 12V DC Harness Junction
11. Expansion Tank Connection
12. Heating Zone Outlet Port
13. Heating Zone Return Port
14. 120V AC Connection
15. Boiler Tank
16. Domestic Hot-Water Coil
17. Interlock Switch
18. Zone Circulation Pump
12 14
Figure 3
Component Cut-Away

Operating the LCD
©Aqua-Hot® 250 Series Propane Service Manual p. 9
Operational Flow Chart
Operational Flow Chart
A heat source is selected from
Interior Switch Panel
Electric Element
Electric Heating Element
will activate, providing
heat to the antifreeze and
water heating solution
within the boiler tank
The burner will begin
providing heat to the
antifreeze and water heating
solution present within the
boiler tank.
The antifreeze and water
heating solution in the boiler
tank heats to 190°F
An Interior Zone
Thermostat Calls
for Heat
A hot water faucet opens,
signaling a need for heat to the
boiler tank
The fl uid circulation pump
activates and begins circulating
the heated antifreeze and water
solution throughout the interior
heating zone
The heating zone
fans activate
Heat is transferred to the
vehicle interior via the heat
exchangers
The cooled antifreeze
is returned to the boiler
tank to be reheated.
Hot water fl ows from the water
faucet
Heat is transferred to the
domestic hot water system
Propane Burner
NOTE: The Burner
and/or Electric
Element (as switched
ON) will automatically
begin reheating the
antifreeze and water
heating solution when
the boiler tank drops
below 155°F.

Controller
©Aqua-Hot® 250 Series Propane Service Manual
p. 10
Relay Control Board
The relay control board at use in your Aqua-Hot 250 Propane
Series is designed to function in conjunction with the Fenwal
Burner Control Card to allow the heater to operate. This section
will introduce you to the basic functions of the board.
Indicator lights line the bottom of the relay control board and
are designated D1 through D6. Each of these lights indicates a
function or event that is taking place. The detailed function of
these lights will be explained on the next page.
• D1: Heating Status Light (orange)
• D2: Electric Element Power (green)
• D3: Pump Power (blue)
• D4: Low-Temperature Cutoff Status (yellow)
• D5: Burner Status (green)
• D6: Interior Zone Heating (orange)
Figure 4
D1 D2 D3 D4 D5 D6
AC Circuit &
Burner Power
Switch Power
Burner
Controller
Power
Fuse Functions, Locations, and Ratings:
There are three fast-blow fuses included with this relay
board and may need to be replaced if they cease to function.
The cradles for these fuses are labeled FH1, FH2, and FH3 and
will contain either a 5A or 10A fuse. The 250P will utilize the 5A
fuse in slot FH3.
• FH1: 10A - AC Activation Circuit and Burner
• FH2: 5A - Switch Power
• FH3: 5A - Burner Controller Power
Note on Diagnosing the Relay Control Board:
If after diagnosing the Aqua-Hot you believe that the
relay control board is at fault, it is very strongly advised that
you contact Aqua-Hot Heating Systems Technical Support to
ensure that the issue has been accurately diagnosed. These
components have a very low rate of failure, and for that reason,
we recommend contacting us before replacing it in an attempt
to reduce down time and unit repair costs.
Relay Control Board

Controller
©Aqua-Hot® 250 Series Propane Service Manual p. 11
Heating Status (D1):
This indicator light will illuminate orange when the burner
and/or electric element switch on the interior switch panel is
ON and the control thermostat is calling for heat.
If the heater is functioning and the light is not illuminated, or
the heater is not functioning and the light is illuminated, there
is an issue with the wiring or one of the components.
Electric Heating Element Status (D2):
This indicator light shows the status of the electric heating
element by illuminating green when the electric element switch
is ON. If the green LED does not illuminate, the electric element
switch is OFF or the unit is low on fl uid.
The D2 light functions with the interior electric element
switch to provide functionality when requested. When the
electric element switch is ON, the D2 light should also be on.
If the D2 indicator light is not illuminated, but the electric
switch on the interior switch panel is in the ON position, there
is a short in the 12V DC side of the electric element circuit. This
could be due to a bad connection, a bad switch, a bad fl uid level
sensor, or the fuse present in FH2 is not functional.
Circulation Pump (D3):
This indicator light shows the power status of the circulation
pump within the Aqua-Hot. The circulation pump is responsible
for circulating fl uid through the heating zone, and stirring the
fl uid within the tank while it is heating.
The system functions correctly if the coach thermostat is
calling for heat, the pump is operating, ad the light is illuminated
blue.
If the light is off while the coach thermostat is calling for
heat or hot water, there may be an issue with the coach wiring
or with the relay control board.
Low-Temperature Cutoff Status (D4):
The low-temp cutoff status thermostat deactivates interior
heat when domestic hot water is being used, and activates the
stir pump in conjunction with the burner switch.
When this light is on, it indicates that there is either a
demand for hot water, or the Aqua-Hot is not yet up to operating
temperature.
NOTE: It is possible for the Electric Heating Element and
Heating Status lights to be illuminated, and the electric
element not function due to an issue with the 110V AC power
supply.
Burner Status (D5):
This indicator light shows the status of the burner by
illuminating green when the burner switch is on.
If the burner switch is in the ON position and the control
thermostat is calling for heat, the D5 indicator light should
illuminate in addition to the D1 heating status light.
If the indicator light remains off while the burner switch is in
the ON position, it could indicate that there is a short present,
the fuse in FH2 may be burned out, or the unit may be low on
fl uid.
Heating Zone Status (D6):
This light indicates that status of the coach thermostat
and the heat exchanger fans. The indicator light will illuminate
orange when the coach thermostat is requesting interior heat,
or hot water is being requested.
If a fault condition occurs, it could be due to a wiring issue, a
faulty thermostat, or issues with the heat exchanger fans.
Relay Control Board

Controller
©Aqua-Hot® 250 Series Propane Service Manual
p. 12
Interior Switch Panel
Introduction:
The interior switch panel is used to control the two heating
sources for the Aqua-Hot’s boiler tank. When a switch is
activated, the indicator light on the switch will illuminate.
Burner Switch:
When the burner switch is in the ON position, the control
thermostat will communicate with the relay control board and
the burner controller that heat is needed for the tank. The
burner will activate and the unit will begin to warm up.
A cold boiler tank can be expected to reach temperature
in approximately 10-20 minutes, depending on the ambient
temperature. In colder temperatures, it may take longer to heat
the unit to its operating temperature.
In order to reach and maintain temperature under all
demands, the burner switch must be in the ON position. Keep
in mind that the electric element is a heat
source. This means that the element can provide hot water
for simple tasks such as hand-washing, and maintaining tank
temperature at times when there is no load. The burner is
intended as the primary heat source.
Additionally, the burner switch can be used to reset a low-
voltage condition. This is accomplished by turning the switch
OFF for 30 seconds, and then turning it back on. This is known
as “power-cycling”.
Electric Element Switch:
When the coach is plugged into an AC power source (i.e.
shore power or a generator) and the electric element switch is
ON, the electric heating element will be used to provide 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 1-2 hours depending on the ambient temperature.
The electric element is intended as a
heating source. If used alone, the electric element will NOT be
able to provide enough heat for continuous hot water or interior
heat.
Interior Switch Panel
Figure 5

Controller
©Aqua-Hot® 250 Series Propane Service Manual p. 13
Exhaust System
Exhaust System Requirements
Introduction:
The Aqua-Hot’s exhaust is hot and must be kept away from any
heat-sensitive material. Therefore, 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 fi re
could result when parked in dry, grassy areas.
• The exhaust must not terminate underneath the vehicle,
underneath an openable window or vent, in the awning
area of the coach (if applicable), or near the slide-out
areas.
• The exhaust must be able to freely exit away from the
vehicle without any obstructions.
• Use standard two-inch automotive-type exhaust piping
and avoid bends if possible.
• The 3-inch and 4-inch black pipe nipple and the exhaust
elbow, originally supplied with the Aqua-Hot must be
used (kit sold separately).
• The exhaust tip must be used to prevent the burner from
extinguishing in winds of up to 40 MPH.
• Mounting must be place every three feet to adequately
support the exhaust system.
• Total exhaust system length must not exceed 30ft in total
length, and shall contain no more than two 90° bends.
#8 x ⅜”
Exhaust Tip
Aqua-Hot’s
Exhaust Pipe
Elbow
Exhaust Pipe
4” Nipple
3” Nipple
Depth of Bay Floor
Mounting Tray Flange
Figure 6
Figure 7

Controller
©Aqua-Hot® 250 Series Propane Service Manual
p. 14
Failure to disconnect all power supplies and/or allow the
unit to cool before servicing could cause serious damage or
personal injury.
Components
Introduction:
This section of the Service Manual details various
components of the Aqua-Hot that may require troubleshooting
and/or replacement in the event of malfunction.
Replacement parts can be ordered online through Aqua-
Hot’s webstore at www.aquahot.com.
If additional assistance is needed, the technical support
team can be contacted at 574-AIR-XCEL (574-247-9235)
Monday through Friday, 7am to 4pm Mountain Standard Time.
Interlock Switch
The interlock switch is a safety device designed to ensure
that the Aqua-Hot’s access cover is securely installed before
the burner will operate.
Troubleshoot the interlock switch if the following conditions
occur:
• The burner fails to operate
• The burner indicator light does not illuminate when the
switch is in the ON position
Troubleshooting:
1. Ensure that the boiler tank has suffi ciently cooled in
order to require heat from the burner.
2. Activate the burner switch located on the interior switch
panel.
3. Locate wires #37 and #24 on the wiring harness as they
lead into the interlock switch.
4. Disconnect the wires from the switch, noting that wire
#24 is connected to the terminal labeled “NO” and #37
is connected to the terminal labeled “COM”.
5. Using an ohmmeter, check the interlock switch for
continuity while the switch button is manually depressed.
6. If continuity is not present with the button pressed in,
follow the instructions in this section to replace the
interlock switch.
Replacement Procedure
1. Disconnect the interlock switch wires by pulling the
quick connectors from the switch spade terminals.
2. Release the interlock switch from the Aqua-Hot cabinet
by pushing in on the locking tabs and pulling the
interlock switch.
3. Remove the defective interlock switch from the Aqua-
Hot.
4. Install the replacement interlock switch into the Aqua-
Hot ensuring that the locking tabs snap into place.
5. Connect the Aqua-Hot’s replacement wires to the
replacement interlock switch with wire #24 connected
to the terminal labeled “NO” and wire #37 connected to
the terminal labeled “COM”.
NOTE: Before attempting to troubleshoot any Aqua-Hot
component, please check all wiring to ensure that there is
no corrosion, loose and/or faulty wiring connection present
which may be causing failure.
Locking Tab
Wire #24
“NO”
Wire #37
“COM”
Button
Figure 8
Figure 9
Interlock
Switch
Interlock Switch

Fluid Level Sensor
©Aqua-Hot® 250 Series Propane Service Manual p. 15
Troubleshooting Guidelines:
Before troubleshooting the fl uid level sensor, ensure that the
following requirements have been met.
• The fl uid expansion bottle is fi lled to at least the “COLD”
mark.
• Verify that all coach-side 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.
• Ensure that the fl uid level sensor is oriented correctly (see
below).
If any of the requirements above are not fulfi lled, correct
them before continuing to diagnose the fl uid level sensor.
Reference the troubleshooting guide below.
Troubleshooting Procedure:
1. Verify that the Aqua-Hot’s expansion bottle is full of
antifreeze and water heating solution.
2. Verify that the wiring is secure, and in good working
condition.
3. Locate the wiring harness for the unit. Find wires #10, #15,
and #16. Wires #10 and #15 will co-terminate in a yellow
connector.
4. Disconnect these wires from th expansion bottle, and test
for continuity across the expansion bottle sensor.
5. If the bottle contains fl uid and continuity does not exist
across the fl uid level sensor, the sensor will need to be
replaced.
Fluid Level Sensor
Introduction:
The fl uid level sensor monitors the current fl uid level within
the Aqua-Hot. This device is intended as a fail-safe measure
which will disengage the Aqua-Hot if the fl uid ever drops below a
set threshold. The fl uid level sensor is located on the expansion
bottle, which is mounted to the side of the unit (see below).
If the fl uid level sensor is malfunctioning, the Aqua-Hot
will show no signs of operation whatsoever. Troubleshoot this
sensor if there is an adequate amount of fl uid present within
the Aqua-Hot, and the unit does not operate:
• The burner fails to operate
• The burner switch indicator light fails to illuminate
• The electric element fails to operate
• The indicator light on the electric switch does not
illuminate
Figure 11
Figure 10
Fluid Level
Sensor
Fluid Return
Hose
Fluid Overfl ow
Hose
Failure to disconnect all power supplies and/or allow the
unit to cool before servicing could cause serious damage or
personal injury.

Fluid Level Sensor
©Aqua-Hot® 250 Series Propane Service Manual
p. 16
Before continuing to the replacement procedure,
ensure that the unit has cooled to ambient temperature,
all power sources have been disconnected, and the
unit is completely shut off.
Replacement Procedure:
In order to replace the fl uid level sensor, the overfl ow bottle
must also be replaced. Please visit www.aquahot.com or call
574-AIR-XCEL (574-247-9235) to order the expansion bottle
kit. Once you have the replacement part in hand, follow the
procedure below.
1. Locate the fl uid expansion bottle.
2. Clamp the overfl ow hose as close to the bottom fi tting as
possible.
3. Grab a bucket or drain receptacle and place it directly
under the lower fi tting of the expansion bottle.
4. Remove the clamp from the lower fi tting of the expansion
bottle.
5. Remove the hose and allow the excess fl uid to drain into
the bucket.
6. Remove the overfl ow hose from the upper fi tting of the
expansion bottle.
7. Remove the old expansion bottle, disconnect the Faston
connectors, and discard the old bottle.
8. Secure the new bottle in position.
9. Crimp the new faston connectors to the new fl uid level
sensor.
10. Connect these wires to their receptacles on the Aqua-Hot
harness.
11. Reconnect the overfl ow hose to the upper fi tting.
12. Reconnect the expansion hose to the lower fi tting.
13. Fill the bottle with the previously drained fl uid.
14. Remove the hose clamps.
15. Test the Aqua-Hot for normal functionality.
If additional assistance is required please contact the Aqua-
Hot Heating Systems Technical support department at 574-AIR-
XCEL (574-247-9235) from 7:00am to 4:00pm MST Monday
through Friday.
Fluid Return Port
Figure 12
Lower Fitting to
Fluid Return Hose
Upper Fitting to
Fluid Overfl ow Hose
Figure 13
Fluid Level
Sensor

Fluid Level Sensor
©Aqua-Hot® 250 Series Propane Service Manual p. 17
If the “Heating Status” (D1) indicator light is not illuminated,
check the following:
• Verify that the temperature of the boiler tank has fallen
below the 175°F minimum operating temperature
by checking with an infrared thermometer. Take the
reading within 12 inches from the painted tank surface
with the thermometer set to “High Emissivity” or similar.
Do not attempt to take readings on a shiny surface.
• If below 175°F, disconnect the control thermostat’s
wires from their connection. Using an ohmmeter, check
for continuity across the control thermostat.
If continuity does not exist across the control thermostat
under these conditions, follow the directions in this section for
replacing the control thermostat.
If continuity exists across this thermostat, inspect it, and the
wiring harness for any damage.
Control Thermostat
Control Thermostat
The control thermostat is installed into 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 Aqua-Hot is
considered to be at operating temperature between 155°F and
188°F. Please reference Page 11 for the relay control board
LED indicator information.
Troubleshooting Conditions:
Troubleshoot the control thermostat if one of the following
conditions has occurred:
• There is a lack of hot domestic water and/or interior
heat.
• The orange heating status light (D1) does not illuminate
while the unit is below 175°F.
Troubleshooting:
1. Verify the following before troubleshooting the control
thermostat:
• The Interlock Switch is depressed (access cover is
properly installed).
• The overfl ow bottle is adequately fi lled.
• The High-Limit Thermostats are not tripped.
• Fuses in the relay control board are functional.
2. Turn the burner and/or electric element switch to the
ON position.
3. Check the relay control board to ensure that “Electric
Heating Element Status” (D2) and/or “Burner Status”
(D5) indicator light is illuminated.
4. Verify that the “Heating Status” (D1) indicator light on
the relay control board is illuminated as it should be
whenever the Aqua-Hot is below 175°F.
NOTE: The Burner and/or Electric Element switch must be
in the ON position for the “Heating Status” indicator light on
the relay control board to illuminate.
Figure 14
Figure 15
Control Thermostat

Fluid Level Sensor
©Aqua-Hot® 250 Series Propane Service Manual
p. 18
Control Thermostat
Failure to disconnect all power supplies and/or allow the
unit to cool before servicing could cause serious damage or
personal injury.
Control Thermostat Replacement Procedure
1. Ensure that the Aqua-Hot has been completely shut
down, all power sources disconnected, and the unit has
been allowed to cool completely.
2. Clamp the hoses indicated below with pinch off pliers to
prevent drainage of the heating zone loop.
3. Drain one gallon of antifreeze and water heating solution
into an external contained to be reused later.
4. Disconnect the defective control thermostat wires by
separating the quick disconnect terminals.
5. Using a ⅞” deep wall socket, unscrew the control
thermostat from the Aqua-Hot’s boiler tank.
6. Wrap the threads of the replacement control thermostat
with 6 wraps of thread seal tape.
7. Reconnect wire #14A and wire #23 to the new control
thermostat.
8. Refi ll the Aqua-Hot’s boiler tank with the previously
drained antifreeze and water heating solution.
9. Refi ll the Aqua-Hot using an external fi ll pump, fi lling
through the zone fi ll port.
10. Test the Aqua-Hot for normal operation.
11. Test the interior heating loop to ensure that there are
no air pockets trapped within the interior heating loop.
12. If necessary, purge the interior heating loop according
to the guide on Page 55.
Hose Pinch-
Off Pliers
Clamp Above Tee
Control Thermostat
Drain Valve
Zone Fill Port
Figure 16
Figure 17

High-Limit Thermostats
©Aqua-Hot® 250 Series Propane Service Manual p. 19
AC High-Limit Thermostat
Introduction:
The AC high-limit thermostat serves as a safety measure
in the event that the electric heating element continues
to operate after the maximum operating temperature has
been reached. The high-limit thermostat allows the current
for the heating element to pass through until the boiler tank
reaches a temperature of 215°F. Should this temperature
be reached, the high-limit thermostat blocks the current to
the element, preventing the element to continue to operate.
Begin troubleshooting the AC High-Limit Thermostat if the
electric element fails to operate correctly.
Troubleshooting Guidelines:
The following conditions must be met before the AC High-
Limit Thermostat can be diagnosed, and if necessary, repaired.
• The fl uid expansion bottle is fi lled 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 verifi ed if the conditions listed above are
not fulfi lled.
Troubleshooting Procedure:
1. Verify the following before troubleshooting the AC high-limit
thermostat:
• The control thermostat is calling for heat.
• The interlock switch is depressed.
• The overfl ow bottle is adequately fi lled.
• The high-limit thermostats are not tripped.
• The fuses in the relay control board are functional.
2. Ensure that the unit has been shut down and completely
cooled before continuing.
3. Shut off the coach-side power breaker to the Aqua-Hot.
4. Disconnect the 3-pin AC Molex plug from the AC relay
enclosure. Leave the DC power supply connected.
5. Activate the “ELECTRIC” switch on the switch panel inside
the coach.
6. Using a multimeter, test for continuity across the AC high-
limit thermostat by placing one lead on the unit-side Molex
connection as shown below.
7. If no continuity exists, locate the AC high-limit thermostat
and depress the center button to reset it. Retest for
continuity.
8. Move the electric switch to the OFF position. Reset for
continuity. If continuity still exists, replace the AC relay.
Figure 19
Figure 18
AC High Limit
Thermostat
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 is tripped, it is
recommended to test the control thermostat and AC relay
for proper operation.
Figure 20

High-Limit Thermostats
©Aqua-Hot® 250 Series Propane Service Manual
p. 20
Replacement Procedure:
If it has been determined that the high-limit thermostat
needs to be replaced, it can be easily replaced by following the
directions below.
1. Shut off gas, electric, and water supply to the Aqua-Hot.
2. Disconnect the domestic water inlet and outlet line fi ttings
from the Aqua-Hot.
3. Unscrew the nut that affi xes the mixing valve to the left side
of the Aqua-Hot cabinet wall.
4. Push down on the mixing valve to expose access to the AC
high-limit thermostat.
5. Cut the wire tie which wraps the wires on the left side of
the unit.
6. Cut the black wires on the AC high-limit thermostat as close
as possible to the body of the thermostat and strip the
other end.
7. Remove the faulty high-limit thermostat using a ⅝” socket
or crow’s foot.
8. Butt-splice a new AC high-limit thermostat to the stripped
wire.
9. Reinstall the AC high-limit thermostat using a ⅝” socket or
crow’s foot.
10. Re-secure the wires using the extra wire tie provided and
reinstall the mixing valve assembly.
11. Make sure the replacement AC high-limit thermostat is
functioning properly by testing for continuity across this
thermostat.
12. Reposition the tempering valve assembly onto its mounting
stud on the left cabinet wall.
13. Re-secure the tempering valve assembly with the previously
removed nut.
14. Reconnect the domestic water connections to the PEX
fi ttings of the tempering valve assembly.
15. Reestablish the gas, electric, and water supply to the Aqua-
Hot.
16. Test for unit for normal operation.
Unscrew this nut
Figure 21
Figure 22