A.O. Smith GTS-305-NE Service Manual
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A.O. Smith GTS-305-NE Service Manual

A.O. Smith GTS-305-NE Service Manual

On-demand gas tankless water heater service manual series 100/101 & series 200/201
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PRINTED 0709
On-Demand Gas Tankless
Water Heater Service Manual
Service information for single and multiple unit installations
for residential, commercial, recirculation and storage tank systems.
Series 100/101 & Series 200/201
ATI-305-N
ATI-305-P
ATO-305-N
ATO-305-P
ATI-505-N
ATI-505-P
ATO-505-N
ATO-505-P
ATI-705-N
ATI-705-P
ATO-705-N
ATO-705-P
ATI-705A-N
ATI-705A-P
ATO-705A-N
ATO-705A-P
GTS-305-NI
GTS-305-PI
GTS-305-NE
GTS-305-PE
GTS-505-NI
GTS-505-PI
GTS-505-NE
GTS-505-PE
GTS-705-NI
GTS-705-PI
GTS-705-NE
GTS-705-PE
GTS-705-NIA
GTS-705-PIA
GTS-705-NEA
GTS-705-PEA
GT-305-NI
GT-305-PI
GT-305-NE
GT-305-PE
GT-505-NI
GT-505-PI
GT-505-NE
GT-505-PE
GT-705-NI
GT-705-PI
GT-705-NE
GT-705-PE
AGT-705-NI
AGT-705-PI
AGT-705-NE
AGT-705-PE
316437-001

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Summary of Contents for A.O. Smith GTS-305-NE

  • Page 1 Water Heater Service Manual Service information for single and multiple unit installations for residential, commercial, recirculation and storage tank systems. Series 100/101 & Series 200/201 ATI-305-N GTS-305-NI GT-305-NI ATI-305-P GTS-305-PI GT-305-PI ATO-305-N GTS-305-NE GT-305-NE ATO-305-P GTS-305-PE GT-305-PE ATI-505-N GTS-505-NI GT-505-NI ATI-505-P GTS-505-PI GT-505-PI...

  • Page 2: Table Of Contents

    Table of Contents General Information..........3-5 PC Board Specifications............6, 7 305e/o, 305i, 505e, 505i ......... 27, 28 Schematic Diagrams..........8, 9 705e/o (ASME ), 705i (ASME) ......29 Fault Isolation............. 10-12 Water Flow Control Assembly Electrical Diagnostic Points 305e, 305i, 505e, 505i ........30, 31 305e/o, 305i, 505e/o 505i ........13, 14 505e, 505i ............

  • Page 3: General Information

    General Information Safety Definitions This is the safety alert symbol. This symbol alerts you to potential hazards that can kill or hurt you and others. Indicates an imminently hazardous situation which, if not avoided, will result in death or DANGER serious injury.

  • Page 4: Service Information

    General Information Service Information The on-demand water heaters must be installed according to all local and state codes or, in the absence of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1 (NFPA 54) - current edition. CSA American, Inc. National Fire Protection Association 8501 East Pleasat Valley Road 1 Batterymarch Park...
  • Page 5 General Information Closed System/Thermal Expansion CAUTION - PROPERTY DAMAGE HAZARD Figure 1a In a closed system use a Typical water piping installation thermal expansion tank As water is heated, it expands (thermal expan- sion). In a closed system, the volume of water Cold Water Pressure Reducing Inlet Valve...

  • Page 6: Specifications

    Specifications Residential Series 100/101* Indoor (i) Input Hot water capacity Efficiency Model Number Min. - Max. Flow Rate Temperature Range @ 45°F Temp. Rise Rating (BTU) 0.6 - 5.3 GPM 15,000 - 199,000 NG 98 -140° F (37 - 60° C) [1] 5.3 GPM (20.1 LPM) (2.3 - 20.1 LPM) 15,000 - 190,000 LP...
  • Page 7 Specifications Residential Series 200/201* Indoor (i) Input Hot water capacity Efficiency Model Number Flow Rate Min. - Max. Temperature Range @ 45°F Temp. Rise Rating (BTU) 0.6 - 7.5 GPM 15,000 - 180,000 6.6 GPM (25.0 LPM) 98 -140° F (37 - 60° C) [1] (2.3 - 28.4 LPM) NG &...

  • Page 8: Schematic Diagrams

    Schematic Diagrams Outdoor Model (NOT PRESENT ON ALL MODELS) (NOT PRESENT ON ALL MODELS) (LOCATED ON BRACKET NEAR FAN ON SOME MODELS) On-Demand Gas Tankless Water Heater Service Manual...
  • Page 9 Schematic Diagrams Indoor Model (NOT PRESENT ON ALL MODELS) (NOT PRESENT ON ALL MODELS) (LOCATED ON BRACKET NEAR FAN ON SOME MODELS) On-Demand Gas Tankless Water Heater Service Manual...

  • Page 10: Fault Isolation

    Fault Isolation The On-Demand water heater 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.
  • Page 11 Fault Isolation Code Fault Remedy No burner operation during Service Call - Check for possible freeze damage to heat exchanger. freeze protection mode Ensure approved venting materials are being used. Air Supply or Exhaust Check that nothing is blocking the flue inlet or exhaust. Blockage Check all vent components for proper connections.
  • Page 12 Fault Isolation Code Fault Remedy 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.

  • Page 13: Electrical Diagnostic Points

    Electrical Diagnostic Points 305e/o, 305i, 505e/o, 505i Wire Color Voltage Resistance Connector No. Pin No.’s (SV1, SV2, SV3, POV) Gas Valve and Modulating Solenoids (Main) Pink - Black 6 ~ 7 o l l 11 - 13 VDC 36.8 - 44.8 ohms (POV) Pink - Pink 2 - 15 VDC 67 - 81 ohms...

  • Page 14: E/O, 305I, 505E/O 505I

    Electrical Diagnostic Points 305e/o, 305i, 505e/o, 505i Wire Color Voltage Resistance Connector No. Pin No.’s Thermal Fuse / Overheat Switch Red - Red 11 - 13 VDC below 1 ohm F6 H1 F6 ~ H12 Flame Rod Place one lead of the meter to the flame rod and the other to ground. With the unit running, 5-150 VAC should be read.

  • Page 15: 705E/O (Asme), 705I (Asme)

    Electrical Diagnostic Points 705e/o (ASME), 705i (ASME) Wire Color Voltage Resistance Connector No. Pin No.’s (SV1, SV2, SV3, POV) Gas Valve and Modulating Solenoids (Main) Pink - Black 24 - 28 ohms 6 ~ 7 37 - 43 ohms 11 - 13 VDC 37 - 43 ohms o l l 37 - 43 ohms...
  • Page 16 Electrical Diagnostic Points 705e/o (ASME), 705i (ASME) Wire Color Voltage Resistance Connector No. Pin No.’s Thermal Fuse / Overheat Switch Red - White 11 - 13 VDC below 1 ohm F6 H1 F6 ~ H12 Flame Rod Place one lead of the meter to the flame rod and the other to ground. With the unit running, 5-150 VAC should be read.

  • Page 17: Wire Diagrams 305E/O, 305I, 505E/O, 505I

    Wiring Diagram 305e/o, 305i, 505e/o, 505i COLOR CODING W :White BY-PASS SERVO MODEL ONLY BK:Black BR:Brown BY-PASS FLOW R :Red CONTROL DEVICE BL:Blue Y :Yellow for REU-EZC P :Pink (Optional) FREEZE PROTECTION O :Orange OPTION G :Green WATER FLOW GY:Gray SENSOR (CN7) MODULATING VALVE...

  • Page 18: 705E/O (Asme), 705I (Asme)

    Wiring Diagram 705e/o (ASME), 705i (ASME) On-Demand Gas Tankless Water Heater Service Manual...

  • Page 19: Flushing The Heat Exchanger

    Flushing the Heat Exchanger 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.

  • Page 20: Component Replacement Instructions

    Component Replacement Instructions 305e/o, 305i, 505e/o, 505i Gas Control Assembly 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Remove four screws securing the front panel. Remove front panel. 4. Pull out wire harness connector at the gas manifold assembly. See Figure 1. 5.

  • Page 21: E/O, 305I, 505E/O, 505I

    Component Replacement Instructions 305e/o, 305i, 505e/o, 505i Gas Control Assembly 12. Attach wire harness to the 4 solenoids as shown in Figure 3 below. o l l SV0 black / pink POV pink / pink (connector not shown) Figure 3 13.

  • Page 22: 705E/O (Asme), 705I (Asme)

    Component Replacement Instructions 705e/o (ASME), 705i (ASME) Gas Control Assembly Bracket screw 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Remove four screws securing the front panel. Remove front panel. 4. On indoor models, remove the bracket holding the controller (1 screw).
  • Page 23 Component Replacement Instructions 705e/o (ASME), 705i (ASME) Gas Control Assembly Failure to correctly assemble the components according to these instructions WARNING could result in a gas leak or explosion. 12. Pull out the gas control assembly. Remove the black / orange wire harness from the 2 solenoids.

  • Page 24: Fan

    Component Replacement Instructions 305e/o, 505e/o 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Turn off the water supply. 4. Remove four screws securing the front panel. Remove front panel. 5. Disconnect wire harness at the fan assembly. Disconnect the air temperature thermistor (two white wires) at the connection with the white and orange wires within the wire bundle.

  • Page 25: 305I, 505I

    Component Replacement Instructions 305i, 505i 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Turn off the water supply. 4. Remove four screws securing the front panel. Remove front panel. 5. Disconnect wire harness at the fan assembly. Disconnect the air temperature thermistor (two white wires) at the connection with the white and orange wires within the wire bundle.

  • Page 26: 705E/O (Asme), 705I (Asme)

    Component Replacement Instructions 705e/o (ASME), 705i (ASME) 1. Turn off the gas supply. Bracket screw 2. Turn off the 120 V power supply. 3. Turn off the water supply. 4. Remove four screws securing the front panel. Remove front panel. 5.

  • Page 27: Pc Board

    Component Replacement Instructions 305e/o, 305i, 505e/o, 505i PC Board 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Turn off the water supply. Figure 15 4. Remove four screws securing the front panel. Screw Remove front panel.
  • Page 28 Component Replacement Instructions 305i, 305e, 505i, 505e 100/101 and 200/201 Series PC Board SW2 setup for 505i SW2 setup for 505e Propane (LPG) Natural Gas (NG) Propane (LPG) Natural Gas (NG) Switch No. Switch No. Switch No. Switch No. SW2 setup for 305i SW2 setup for 305e Propane (LPG) Natural Gas (NG) Propane (LPG) Natural Gas (NG)

  • Page 29: 705E/O (Asme), 705I (Asme)

    Component Replacement Instructions 705e/o (ASME), 705i (ASME) PC Board Figure 16 1. Turn off the gas supply. Screw 2. Turn off the 120 V power supply. Burner test point 3. Remove four screws securing the front panel. Remove front panel. Potentiometer 4.

  • Page 30: Water Flow Control Assembly

    Component Replacement Instructions 305e/o, 305i, 505e/o, 505i 100/101 and 200/201 Series Water Flow Control Assembly Due to design changes, the new valve may appear different than the installed valve in NOTICE color, size, and in the number of wires in the harness connections. 1.

  • Page 31: 305E, 305I, 505E, 505I

    Component Replacement Instructions 305e, 305i, 505e, 505i 100/101 and 200/201 Series Water Flow Control Assembly 7. Pull out the water flow servo assembly and disconnect the cable harnesses. (Figure 19) A.water flow sensor harness (black/yellow/red wires) B.water flow servo harness (red/blue/brown/yellow/gray or red/blue/brown/orange/yellow/gray wires) C.heating element water flow servo connector Figure 19...
  • Page 32 Component Replacement Instructions 505e/o, 505i 100/101 and 200/201 Series Water Flow Control Assembly Due to design changes, the new valve may appear different than the installed valve in NOTICE color, size, and in the number of wires in the harness connections. 1.

  • Page 33: 505E, 505I

    Component Replacement Instructions 505e, 505i 100/101 and 200/201 Series Water Flow Control Assembly Figure 22 11. Remove the 4 screws attaching the water inlet to the underneath side of the water heater. Water inlet 12. Disconnect the cable harnesses (Figure 23): a.

  • Page 34: 705E/O (Asme), 705I (Asme)

    Component Replacement Instructions 705e/o (ASME), 705i (ASME) Water Flow Control Assembly 1. Turn off the gas supply. 2. Turn off the 120 V power supply. Water 3. Turn off the water supply. Drain all water from the lines appliance. 4. Remove four screws securing the front panel. Remove front panel.
  • Page 35 Component Replacement Instructions 305e Heat Exchanger 1. Turn off the gas supply. Burner cover 2. Turn off the 120 V power supply. plate 3. Turn off the water supply. Drain all water from the appliance. Gas Manifold 4. Remove four screws securing the front panel. Remove front panel.

  • Page 36: Heat Exchanger 305E

    Component Replacement Instructions 305e Heat Exchanger Disconnect PC Board (Figure 31) 11. Remove 1 screw connecting the PC Board to the heat exchanger assembly. Remove Gas Manifold (Figure 31) 12. Remove the 6 screws that attach the gas Ignition line manifold to the combustion chamber (part of the heat exchanger assembly).
  • Page 37 Component Replacement Instructions 305e Heat Exchanger Failure to correctly assemble the components according to these instructions WARNING could result in a gas leak or explosion. Installation 21. Install the largest O-ring (included in kit) over the water outlet tube and the two smaller O-rings (included in kit) over the bypass servo tubes.

  • Page 38: 505E/O

    Component Replacement Instructions 505e/o Figure 36 Heat Exchanger Burner cover plate 1. Turn off the gas supply. 2. Turn off the 120 V power supply. Gas Manifold 3. Turn off the water supply. Drain all water from the appliance. 4. Remove four screws securing the front panel. PC Board Remove front panel.
  • Page 39 Component Replacement Instructions 505e/o Heat Exchanger Disconnect PC Board (Figure 39) Figure 39 11. Remove 1 screw connecting the PC Ignition line Board to the heat exchanger assembly. 6 screws (gas manifold) Remove Gas Manifold (Figure 39) PC Board screw 12.
  • Page 40 Component Replacement Instructions 505e/o Heat Exchanger Failure to correctly assemble the components according to these instructions WARNING could result in a gas leak or explosion. Installation 20. Remove 2 screws above the exhaust. Pull assembly from the unit. (Figure 42) 21.

  • Page 41: 305I

    Component Replacement Instructions 305i Heat Exchanger 1. Turn off the gas supply. 2. Turn off the 120 V power supply. Figure 44 3. Turn off the water supply. Drain all water from the appliance. 4. Remove four screws securing the front panel. Burner cover Remove front panel.
  • Page 42 Component Replacement Instructions 305i Heat Exchanger Remove Gas Manifold (Figure 46) 13. Remove the 6 screws that attach the gas manifold to the combustion chamber (part of the heat exchanger assembly). 14. Remove the 3 screws that attach the gas manifold to the gas valve. These screws are machine screws and must be used at these locations.
  • Page 43 Component Replacement Instructions 305i Heat Exchanger Disconnect Wire Harness Attachments 19. Remove the wire harness attachments - sensors, heating elements, fusible link brackets. Ensure that the small O-ring in the thermistor is removed. Remove Heat Exchanger and Air Intake/Exhaust 20. Remove 8 screws connecting the assembly to the water heater casing assembly. (Figures 48, 49) Near fan assembly location At right and left upper corners of water heater Figure 48...
  • Page 44 Component Replacement Instructions 305i Heat Exchanger Install Packings and Bracket 26. Install the O-ring (included in kit) over the water outlet tube and the O-ring (included in kit) over the water flow servo tube. (Figure 45) 27. Install the bracket over the replacement heat exchanger. Push evenly on both sides of the bracket. Attach with four screws.

  • Page 45: 505I

    Component Replacement Instructions 505i Heat Exchanger 1. Turn off the gas supply. Figure 55 2. Turn off the 120 V power supply. 3. Turn off the water supply. Drain all water from the appliance. Burner cover 4. Remove four screws securing the front panel. plate Remove front panel.
  • Page 46 Component Replacement Instructions 505i Heat Exchanger Disconnect Water Lines (Figure 57) 10. Remove 1 screw from the water outlet bracket. Remove the bracket by rotating and moving it up toward the bend in the tube where the diameter is smaller. 11.
  • Page 47 Component Replacement Instructions 505i Heat Exchanger Remove Burner and Burner Cover Plate (Figure 59) 16. Remove the 8 screws attaching the burner cover plate to the combustion chamber. Move the cover plate to the side. It is not necessary to disconnect the wire harness from the burner cover plate. 17.
  • Page 48 Component Replacement Instructions 505i Heat Exchanger Remove Heat Exchanger and Air Intake/Exhaust 20. Remove 8 screws connecting the assembly to the water heater casing assembly. (Figures 61, 62) Near fan assembly location At right and left upper corners of water heater Figure 61 3 screws 2 screws...
  • Page 49 Component Replacement Instructions 505i Heat Exchanger Combine the Heat Exchanger and the Air Intake/Exhaust 28. Push the heat exchanger into the air intake/exhaust assembly. Attach with four screws. (Figure 64) 29. Attach the cover plate over the air intake passage with 9 screws. (Figure 63) Install Heat Exchanger and Air Intake/Exhaust Assembly (Figures 61, 62) 30.

  • Page 50: 705E/O (Asme)

    Component Replacement Instructions 705e/o (ASME) Heat Exchanger 5 screws 2 machine screws (gas manifold) (gas valve) 1. Turn off the gas supply. 2. Turn off the 120 V power supply. 3. Turn off the water supply. Drain all water from the appliance. 4.

  • Page 51: E/O (Asme)

    Component Replacement Instructions 705e/o (ASME) Heat Exchanger 4 locations 15. Remove the fan assembly (4 screws) and install it on the new heat exchanger. (Figure 71) 16. Remove the flue outlet (6 screws) and install it on the new heat exchanger. (Figure 72) 17.

  • Page 52: Asme)

    Component Replacement Instructions 705i (ASME) Heat Exchanger 1. Turn off the gas supply. Bracket screw 2. Turn off the 120 V power supply. 3. Turn off the water supply. Drain all water from the appliance. 4. Remove four screws securing the front panel.
  • Page 53 Component Replacement Instructions 705i (ASME) Heat Exchanger 14. Remove the 3 screws at the seal plate at the top of the water heater. Remove the seal plate and gasket. (Figure 79) 15. Remove flue outlet vent (4 screws). (Figure 80) 16.
  • Page 54 Component Replacement Instructions 705i (ASME) Heat Exchanger 24. Insert the burner and place the burner cover plate into position. Attach the burner cover plate first with 9 screws and then attach the burner with 2 screws. (Figure 78) 25. Replace the electrode gasket. (Figure 83) 26.

  • Page 55: Gas Pressure Setting Procedure

    Gas Pressure Setting Procedure CAUTION Do not touch the areas at or near the heat exchanger or combustion chamber. These areas become very hot and could cause burns. 1. Remove the front panel (four screws). 2. Calibrate the low fire and high fire settings as follows: A.

  • Page 56: Gas Pressure Setting Procedure

    Gas Pressure Setting Procedure Figure 88 B. Turn on the gas supply. C. Turn on the power supply. D. Flow water through the water heater at the maximum flow rate obtainable. (At least 3 gallons per minute is recommended.) E. Move No. 7 dip switch of the SW1 bank to the ON position to calibrate “Forced Low”...

  • Page 57: Manifold Pressure Settings

    Manifold Gas Pressure Settings 100/101 and 200/201 Series Natural Gas Propane Gas (Inch - W.C.) (Inch - W.C.) Altitude High Fire Low Fire High Fire Low Fire 305e/o 0.56 0.88 505e/o 0.56 0.88 705e/o (ASME) 0.65 0.80 less than 10200 ft (3109 m) 305i 0.52...

  • Page 58: Dip Switch Settings

    Dip Switch Settings 100/101 and 200/201 Series SW2 Bank (present on replacement PC boards only) SW1 Bank OFF - Propane Gas OFF - “Long Flue” ON - Natural Gas ON - “Short Flue” and Outdoor Models OFF - Outdoor model “Long flue”...
  • Page 59 Notes On-Demand Gas Tankless Water Heater Service Manual...
  • Page 60 • 500 Tennessee Waltz Parkway • Ashland, TN 37015 •...

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