A.O.Smith 305, 505, 705 Operation and Installation Manual
Direct Vent Tankless Water Heater
Operation and Installation Manual
Models:
305
505
705
FOR INDOOR APPLICATIONS ONLY
Table of Contents.................... 2
Consumer Safety Information.. 4
Operating Instructions ............. 5
Maintenance............................ 8
Error Codes............................. 9
ANS Z21.10.3
●
CSA 4.3
Installation Instructions............ 13
Warranty ................................. 38
INSTALLER: Leave this manual with the appliance.
CONSUMER: Retain this manual for future reference.
WARNING: If the information in these instructions is not
followed exactly, a fire or explosion may result causing
property damage, personal injury or death.
— Do not store or use gasoline or other flammable vapors and
liquids in the vicinity of this or any other appliance.
— WHAT TO DO IF YOU SMELL GAS
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any phone in
your building.
• Immediately call your gas supplier from a neighbor’s phone.
Follow the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the fire
department.
— Installation and service must be performed by a qualified
installer, service agency or the gas supplier.
Table of Contents
Specifications ......................................................3
Consumer Safety Information
Safety Definitions .............................................4
Safety Behaviors and Practices .......................4
Safety Features ................................................4
Description of Operation ....................................5
Operating Instructions
Features Available on Remote Controller ........5
Setting the Temperature...................................6
Temperature Options Without
a Remote Controller .........................................6
Temperature Ranges .......................................7
Setting Controller to Mute.................................7
Maintenance
Cleaning.......................................................8
Vent System.................................................8
Motors ..........................................................8
Remote Controller........................................8
Lime / Scale Buildup ....................................8
Snow Accumulation .....................................8
Visual Inspection of Flame...........................8
Error Codes
Error Code Table........................................9, 10
Trouble Shooting for Common Issues............11
Accessing Operating Information ...................11
Water Quality..................................................11
Flushing the Heat Exchanger.........................12
(Error Code: LC or 00)
Installation Instructions....................................13
General Instructions .......................................13
Clearances from Appliance ............................ 14
Attachment of the Water Heater.....................14
Electrical Connection .....................................15
Gas Piping
General Instructions.................................15
Pipe Sizing Procedure - Example ............16
Water Piping
General Instructions.................................17
Pressure Relief Valve ..............................17
Freeze Protection.....................................17
Freeze Protection Piping ................................18
Recommended Piping for Basic Installation ..19
Recommended Piping for
Circulation Systems .......................................20
Optional Piping for Circulation Systems.........21
Venting Instructions
Intake / Exhaust Guidelines .....................22
Condensate..............................................22
Maximum Vent Length .............................23
Vent Products ..........................................24
Flue Terminal Clearances
(ANS Z21.10.3 ● CSA 4.3
Additional Clearances - Vent Terminal...........26
Flue Installation for 305 and 505 Models ......27
Flue Installation for 705 Model .................28, 29
High Altitude Installation.................................30
Connecting Multiple Water Heaters................30
Remote Controller Installation
Location....................................................31
Configurations ..........................................31
Cable Lengths and Size...........................31
Mounting the Controller............................ 32
Operating Instructions ....................................33
Technical Data
Pressure Drop Curve .....................................34
Outlet Flow Data.............................................34
Space Heating ................................................35
Dimensions.....................................................36
Ladder Diagram..............................................37
Warranty .......................................................38, 39
).............................25
2 305, 505, 705 Indoor Manual
Specifications
Model
Minimum Gas Consumption Btu/h
Maximum Gas Consumption Btu/h
Hot water capacity (Min - Max) *
Hot water capacity (45°F rise) 5.3 GPM (20.1 L/min)
Default Temperature Setting (no controller) 120º F (49º C)
Remote Controller Default Temperature
Setting
Maximum Temp Setting (Commercial**) 160º F (71º C) 185º F (85º C)
Maximum Temp Setting (Residential) 140º F (60º C)
Minimum Temperature Setting 98º F (37º C)
Weight 50 lb (23 kg) 55 lb (25 kg)
Efficiency Rating - Propane Gas 84%
Noise level 49 dB
Electrical
Consumption
By-Pass Control Fixed
Minimum Gas Supply
Pressure
Maximum Gas Supply
Pressure
Type of Appliance Direct Vent, Temperature controlled continuous flow gas hot water system.
Operation With or without remote controls, mounted in kitchen, bathroom, etc.
Approved Gas Type Natural Gas or Propane - Ensure unit matches gas type it's being installed on.
Connections Gas Supply: 3/4" MNPT, Cold Water Inlet: 3/4" MNPT, Hot Water Outlet: 3/4"
Ignition System Direct Electronic Ignition
Electric Connections Appliance: AC 120 Volts, 60Hz. Remote Control: DC 12 Volts (Digital)
Water Temperature Control Simulation Feedforward and Feedback.
Water Supply Pressure Minimum Water Pressure: 20 PSI (Recommended 30-80 PSI for maximum
Maximum Water Supply Pressure 150 PSI
Remote Control Cable Non-Polarized Two Core Cable (Minimum 22 AWG)
Normal 79 W 99 W
Standby 2.8 W 2 W
Anti-frost Protection
Natural Gas 5.0 inch W.C.
Propane 8.0 inch W.C.
Natural Gas 10.5 inch W.C.
Propane 13.5 inch W.C.
305
199,000 Natural Gas
190,000 Propane Gas
0.6 - 5.3 GPM
(2.3 - 20.1 L/min)
505 705
15,000 19,000
237,000
0.6 - 8.5 GPM
(2.3 - 32.0 L/min)
7.4 GPM (28.0 L/min)
Natural Gas
7.1 GPM (26.9 L/min)
Propane Gas
104º F (40º C)
100 W 116 W
Electronic
0.6 - 9.8 GPM
(2.3 - 37 L/min)
8.8 GPM (33.5 L/min)
* Minimum flow may vary slightly depending on the temperature setting and the inlet water temperature.
** for commercial and hydronic applications requiring higher temperatures
Specifications are subject to change without prior notice.
The maximum inlet gas pressure must not exceed the value specified by the manufacturer. The minimum value
listed is for the purpose of input adjustment.
305, 505, 705 Indoor Manual 3
Consumer Safety Information
Safety Definitions
This is the safety alert symbol. This symbol alerts you to potential hazards that can kill or hurt you and
others.
DANGER
WARNING
CAUTION
Indicates an imminently hazardous situation which, if not avoided, will result in death or
serious injury.
Indicates a potentially hazardous situation which, if not avoided, could result in death or
serious injury.
Indicates a potentially hazardous situation which, if not avoided, could result in minor or
moderate injury. It may also be used to alert against unsafe practices.
Safety Behavior and Practices
WARNING
• Keep the area around the appliance clear and free
from combustible materials, gasoline, and other
flammable vapors and liquids.
• Do not use this appliance if any part has been under
water. Immediately call a qualified service
technician to inspect the appliance and to replace
any part of the control system and any gas control
which has been under water.
• This appliance is equipped with a three-prong plug
for your protection against shock hazard and should
be plugged directly into a properly grounded threeprong receptacle. Do not cut or remove the ground
prong from this plug.
• Any alteration to the appliance or its controls can be
dangerous and will void the warranty.
• Always check the water temperature before entering
a shower or bath.
Safety Features
• Overheat: The appliance will automatically shut
down when the appliance exceeds a predetermined
temperature.
• Flame Failure: The appliance will automatically
shut down if the burner flame is extinguished.
• Power Failure: The appliance will cut off the gas if
it loses electrical power.
• Power Surge Fuse: A glass fuse protects against
overcurrent. If the fuse blows then all indicator
lamps will be off.
• Fusible Link: In case the overheat feature does
not prevent the temperature from rising then the
fusible link will break shutting off the appliance.
4 305, 505, 705 Indoor Manual
Description of Operation
This appliance is one of the most advanced water
heaters available. It provides a continuous supply of
hot water at a preset temperature. This appliance is
direct vent where air is brought in from the outside and
combustion gases are exhausted to the outside.
While electricity, water, and gas supplies are
connected, this appliance produces hot water
whenever a hot water tap is open.
Ignition is electronic. There is no pilot light consuming
gas while the water heater is not being used. The gas
burner lights automatically when the hot water tap is
opened and goes out when the tap is closed.
Installation of the remote controller is highly
recommended. The remote controller can set the
temperature within a specific range and can provide
error codes to diagnose any problems.
The temperature of the outgoing hot water is constantly
monitored. This appliance may adjust the water flow in
order to maintain the temperature setting. The water
flow may vary from summer to winter due to the
difference in ground water temperature.
Operating Instructions
Features Available on Remote Controller
The remote controller is supplied with the appliance. Dimensions (inches): 3.5 W x 4.75 H x 0.75 D
In Use
Indicator
Priority
Indicator
Temperature
Display
Priority
Button
Thermostat
ON/OFF
Button
Features
Error Codes When a fault is detected an error code flashes at the temperature
In Use Indicator Indicates that hot water is being supplied (i.e. a hot water tap is
open).
ON/OFF Button Used to turn the water heater ON or OFF.
Priority Button /
Indicator
Temperature Display Shows the temperature setting.
Thermostat Increases or decreases the temperature setting.
Indicates that this controller is setting the temperature . Priority
can be switched to another controller by pressing its Priority
Button when no hot water is running.
Description
305, 505, 705 Indoor Manual 5
Setting the Temperature
DANGER
1. Press the “Priority button” on the
remote controller. The green
Priority light will glow indicating
that this controller is controlling
the temperature and that the
water heater is ready to supply
hot water.
The priority can only be changed
while no hot water is running.
Hot water can be dangerous, especially for infants or children, the elderly,
or infirm. There is hot water scald potential if the thermostat is set too high.
Water temperatures over 125º F (51º C) can cause severe burns or
scalding resulting in death.
Hot water can cause first degree burns with exposure for as little as:
3 seconds at 140º F (60º C)
20 seconds at 130º F (54º C)
8 minutes at 120º F (48º C)
Test the temperature of the water before placing a child in the bath or
shower.
Do not leave a child or an infirm person in the bath unsupervised.
NOTICE
While any hot water is being
provided, the temperature setting can
only be adjusted between 98º F and
110º F.
NOTICE
Check local codes for the maximum
water temperature setting allowed
when used in nursing homes,
schools, day care centers, and all
other public applications.
2. Press the ▲ or ▼ buttons to
obtain the desired temperature
setting.
All hot water sources are able to
NOTICE
If a newly installed unit with a remote
controller has not been powered for
at least 6 hours then the temperature
will return to the default setting of
104º F (40º C) if power is interrupted.
provide water at this temperature
setting until it is changed again at
this or another remote controller.
NOTICE
There may be a variation between
the temperature displayed on the
remote controller and the
temperature at the tap due to
weather conditions or the length of
pipe to the water heater.
Temperature Options Without a Remote Controller
The default temperature setting for this appliance
installed without a remote controller is 120º F (49º C).
If desired the temperature setting can be changed to
140º F (60º C) by adjustment of a dip switch.
Set dip switch 5 to ON to obtain 140º F water
temperature setting.
Set dip switch 5 to OFF (default) to obtain 120º F
water temperature setting.
WARNING
DO NOT adjust the other dip
switches unless specifically
instructed to do so.
120º F (49º C) 140º F (60º C)
Switch No.
ON
O
F
F
1
2
3
4
5
6
7
8
Switch No.
ON
O
F
F
1
2
3
4
5
6
7
8
6 305, 505, 705 Indoor Manual
Temperature Ranges
This water heater will attempt to provide hot water at the temperature setting even when the water flow is varied
or when more than 1 tap is in use. The water heater can deliver water at only one temperature setting at a time.
The available temperatures for a given model are provided below.
Model Temperature Settings Available (ºF)
305
505
705
Temp in Celsius ºC 37 38 39 40 41 42 43 46 49 52 54 57 60
* These settings require the commercial controller which is for commercial and hydronic applications requiring
higher temperatures. When the commercial controller is connected, these higher temperatures are available
on all controller models in the system.
If a space heating application requires temperatures higher than 140º F then a mixing valve shall be installed to
temper the water temperature to 140º F or less for domestic use.
Suggested temperatures are
• Kitchen 120 ºF (49º C)
• Shower 98º - 110º F (37º - 43º C)
To change the temperature scale from Celsius to Fahrenheit or vice versa, press and hold the “On/Off” button for
5 seconds while the water heater is OFF.
98 100 102 104 106 108 110 115 120 125 130 135 140
98 100 102 104 106 108 110 115 120 125 130 135 140
These temperatures are suggestions only.
A temperature lower than 98º F (37º C) can be
obtained at the tap by mixing with cold water.
* * *
150 160
150 160 185
66 71 85
Setting Controller to Mute
To eliminate the beeps when keys are pressed or to turn the beeps back on, press and hold both the ▲and ▼
buttons until a beep is heard (approximately 5 seconds).
305, 505, 705 Indoor Manual 7
Maintenance
WARNING
Turn off the electrical power supply, the manual gas
valve and the manual water control valve whenever
servicing the unit.
Repairs and maintenance should be performed by a
qualified service technician. The appliance should be
inspected annually by a qualified service technician.
Verify proper operation after servicing.
Cleaning
It is imperative that control compartments, burners,
and circulating air passageways of the appliance be
kept clean.
Clean as follows:
1. Turn off and disconnect electrical power. Allow to
cool.
2. Remove and clean the water inlet filter.
3. Remove the front panel by removing 4 screws.
4. Use pressurized air to remove dust from the main
burner, heat exchanger, and fan blades. Do not
use a wet cloth or spray cleaners on the burner.
Do not use volatile substances such as benzene
and thinners. They may ignite or fade the paint.
Snow Accumulation
Keep the area around flue terminal free of snow and
ice. The appliance will not function properly if the
intake air or exhaust is impeded (blocked or partially
blocked) by obstructions.
Visual Inspection of Flame
The burner must flame evenly over the entire surface
when operating correctly. The flame must burn with a
clear, blue, stable flame. See the parts breakdown of
the burner for the location of the view ports.
The flame pattern should be as shown in the figures
below.
5. Use soft dry cloth to wipe cabinet.
Vent System
The vent system should be inspected at least annually
for blockages or damage.
Motors
Motors are permanently lubricated and do not need
periodic lubrication. Keep fan and motor free of dust
and dirt by cleaning annually.
Remote Controller
Use a soft damp cloth to clean the remote controller.
Do not use solvents.
Lime / Scale Build-up
If you receive Error Code “LC”, refer to the procedure,
Flushing the Heat Exchanger. Refer to the section on
Water Quality to see if your water needs to be treated
or conditioned. (When checking maintenance code
history, “00” is substituted for “LC”.)
8 305, 505, 705 Indoor Manual
Error Codes
This appliance has the ability to check its own operation continuously. If a fault occurs, an error code will flash on
the Display of the remote controller. This assists with diagnosing the fault and may enable you to overcome a
problem without a service call. Please identify the code displayed when inquiring about service.
WARNING
Some of the checks below may need to be done by a qualified service technician. Call a
service technician for any remedy that involves gas or electricity. Call a service
technician if you have any doubt or reservation about performing the remedy yourself.
Error Code Table
Code Fault Remedy
02
10
11
12
No burner operation during
freeze protection mode
Air Supply or Exhaust
Blockage
No Ignition Check that the gas is turned on at the water heater, gas meter, or cylinder.
Flame Failure Check that the gas is turned on at the water heater and gas meter. Check for
Service Call
Ensure approved venting materials are being used.
Check that nothing is blocking the flue inlet or exhaust.
Check all vent components for proper connections.
Ensure vent length is within limits.
Ensure condensation collar was installed correctly.
Verify dip switches are set properly.
Check fan for blockage.
Ensure gas type and pressure is correct.
Ensure gas line, meter, and/or regulator is sized properly.
Bleed all air from gas lines.
Verify dip switches are set properly.
Ensure appliance is properly grounded.
Disconnect all 2-Unit or Multi-Unit connections to isolate the problem.
Ensure igniter is operational.
Check igniter wiring harness for damage.
Check gas solenoid valves for open or short circuits.
Remove burner cover and ensure all burners are properly seated.
Remove burner plate and inspect burner surface for condensation or debris.
obstructions in the flue outlet.
Ensure gas line, meter, and/or regulator is sized properly.
Ensure gas type and pressure is correct.
Bleed all air from gas lines.
Ensure proper venting material was installed.
Ensure condensation collar was installed properly.
Ensure vent length is within limits.
Verify dip switches are set properly.
Ensure appliance is properly grounded.
Disconnect keypad.
Disconnect all 2-Unit or Multi-Unit connections to isolate the problem.
Check power supply for loose connections.
Check power supply for proper voltage and voltage drops.
Ensure flame rod wire is connected.
Check flame rod for carbon build-up.
Disconnect and reconnect all wiring harnesses on unit and PC board.
Check all components for electrical short.
Check gas solenoid valves for open or short circuits.
Remove burner plate and inspect burner surface for condensation or debris.
305, 505, 705 Indoor Manual 9
Error Code Table
Code Fault Remedy
14
16
32
33
34
52
61
71
72
LC
No
code
Thermal Fuse Check gas type of unit and ensure it matches gas type being used.
Check for restrictions in air flow around unit and vent terminal.
Check for low water flow in a circulating system causing short-cycling.
Ensure dip switches are set to the proper position.
Check for foreign materials in combustion chamber and/or exhaust piping.
Check heat exchanger for cracks and/or separations.
Check heat exchanger surface for hot spots which indicate blockage due to scale build-
up. Refer to instructions in manual for flushing heat exchanger.
Measure resistance of safety circuit.
Ensure high fire and low fire manifold pressure is correct.
Check for improper conversion of product.
Over Temperature
Warning
Outgoing Water
Temperature Sensor
Fault
Heat Exchanger
Outgoing Temperature
Sensor Fault
Combustion Air
Temperature Sensor
Fault
Modulating Solenoid
Valve Signal Abnormal
Combustion Fan
Failure
SV0, SV1, SV2, and
SV3 Solenoid Valve
Circuit Fault
Flame Sensing Device
Fault
Scale Build-up in Heat
Exchanger (when
checking maintenance
code history, “00” is
substituted for “LC”)
Nothing happens when
water flow is activated.
Check for restrictions in air flow around unit and vent terminal.
Check for low water flow in a circulating system causing short-cycling.
Check for foreign materials in combustion chamber and/or exhaust piping.
Check for clogged heat exchanger.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
Check for restrictions in air flow around unit and vent terminal.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Ensure fan blade is tight on motor shaft and is in good condition.
Replace sensor.
Check modulating gas solenoid valve wiring harness for loose or damaged terminals.
Measure resistance of valve coil.
Ensure fan will turn freely.
Check wiring harness to motor for damaged and/or loose connections.
Measure resistance of motor winding.
Check wiring harness to all solenoids for damage and/or loose connections.
Measure resistance of each solenoid valve coil.
Ensure flame rod is touching flame when unit fires.
Check all wiring to flame rod for damage.
Remove flame rod and check for carbon build-up; clean with sand paper.
Check inside burner chamber for any foreign material blocking flame at flame rod.
Measure micro amp output of sensor circuit with flame present.
Replace flame rod.
Flush heat exchanger. Refer to instructions in manual.
Replace heat exchanger.
Clean inlet water supply filter.
On new installations ensure hot and cold water lines are not reversed.
Check for bleed over. Isolate unit from building by turning off hot water line to building.
Isolate the circulating system if present. Open your pressure relief valve; if water is
flowing, there is bleed over in your plumbing.
Ensure you have at least the minimum flow rate required to fire unit.
Ensure turbine spins freely.
Measure the resistance of the water flow control sensor.
Check for DC shorts at components.
10 305, 505, 705 Indoor Manual
Trouble Shooting for Common Issues
I don’t have any hot water when I open the tap.
Make sure there is gas, water, and electricity to the
water heater (power is turned on and the gas is turned
on).
When I was using the hot water, the water got cold.
If you adjusted the flow from the tap to lessen it, you
may have gone below the minimum flow required. This
water heater requires a minimum flow rate to operate.
(See the specification page for the flow rate of your
model.) Decrease the temperature setting at the
remote controller or increase the water flow.
White smoke comes out of the exhaust.
During colder weather when the exhaust temperature
is much hotter than the outside air, the exhaust fumes
condense producing water vapor.
When I open a hot tap, I do not immediately get hot
water.
Hot water must travel through your plumbing from the
water heater to the faucet. The time period for hot
water to reach your fixture is determined by the amount
of water in the plumbing system between the water
heater and the fixture, water pressure, and the flow
rate of the fixture.
After I turn off the hot water tap, the fan on the
water heater continues to run.
The fan is designed to continue running for a short time
after the flow of water stops. This is to ensure constant
water temperatures during rapid starting and stopping,
as well as exhausting any residual gas flue products
from the unit.
Accessing Operating Information
To display the most recent error codes press and hold the “On/Off” button for 2 seconds. While holding the “On/
Off” button press the ▲ button. The last 9 error codes will flash one after the other. To exit this mode press the
“On/Off” and ▲ button as before.
To display the water flow through the water heater press and hold the ▲ button for 2 seconds and without
releasing the ▲ button press the “On/Off” button.
To display the outlet water temperature press and hold the ▼ button for 2 seconds and without releasing the ▼
button press the “On/Off” button.
Water Quality
Consideration of care for your water heater should
include evaluation of water quality. If the water quality
exceeds the target levels provided in the table, you
may want to treat or condition the water.
* Source: Part 143 National Secondary Drinking Water
Regulations
Total Hardness Up to 200 mg / L
Aluminum * Up to 0.2 mg / L
Chlorides * Up to 250 mg / L
Copper * Up to 1.0 mg / L
Iron * Up to 0.3 mg / L
Manganese * Up to 0.05 mg / L
Maximum Level
pH * 6.5 to 8.5
TDS (Total Dissolved
Solids) *
Zinc * Up to 5 mg / L
305, 505, 705 Indoor Manual 11
Up to 500 mg / L
y
Flushing the Heat Exchanger (Error Code: LC or 00)
An “LC” or “00” error code indicates the unit is beginning to lime up and must be flushed. Failure to flush the
appliance will cause damage to the heat exchanger. Damage caused by lime build-up is not covered by the unit’s
warranty. After flushing, reset the LC fault code by turning off the power to the unit and turning the power back
on.
1. Disconnect electrical power to the water heater.
2. Close the shutoff valves on both the hot water and cold
water lines (V3 and V4).
3. Connect pump outlet hose (H1) to the cold water line at
service valve V2.
4. Connect drain hose (H3) to service valve V1.
5. Pour approximately 4 gallons of virgin, food grade, white
vinegar or citric acid into pail.
Water Heater
6. Place the drain hose (H3) and the hose (H2) to the pump
inlet into the cleaning solution.
7. Open both service valves (V1 and V2) on the hot water and
cold water lines.
8. Operate the pump and allow the cleaning solution to
circulate through the water heater for at least 45 minutes.
9. Turn off the pump.
10. Rinse the cleaning solution from the water heater as follows:
a. Remove the free end of the drain hose (H3) from the pail.
n
b. Close service valve, (V2), and open shutoff valve, (V4).
Do not open shutoff valve, (V3).
I
n
i
e
l
e
t
r
l
F
i
G
a
s
S
c. Allow water to flow through the water heater for 5 minutes
d. Close service valve, (V1), and open shutoff valve, (V3).
11. Disconnect all hoses.
V1
V2
12. Remove the in-line filter at the cold water inlet and clean out
any residue. Place filter back into unit.
13. Restore electrical power to the water heater.
H3
V4
V3
u
p
p
l
C
o
W
d
H
o
t
W
n
a
e
i
t
r
L
e
l
r
L
n
e
a
i
e
t
H2
5 gallon pail of virgin, food
grade, white vinegar (or virgin,
food grade, citric acid).
Circulating Pump
KEY
3/4" Ball Valve
3/4" Union
Check Valve
Pressure Relief Valve
Pressure Regulator
Circulating Pump
Boiler Drain Valve
S
Solenoid Valve
12 305, 505, 705 Indoor Manual
H1
Loading...