A.O. Smith SERIES 120 Service Handbook
A.O. Smith SERIES 120 Service Handbook

A.O. Smith SERIES 120 Service Handbook

Commercial gas water heaters
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Service Handbook
COMMERCIAL GAS WATER HEATERS
MODEL BTR 500/A SERIES 120/121
INSTALLATION CONSIDERATIONS - PRE SERVICE
INSTALLATION CONSIDERATIONS - PRE SERVICE
CHECKS - OPERATION & SERVICE -TROUBLESHOOTING
CHECKS - WATER HEATER CONSTRUCTION -
OPERATION & SERVICE - TROUBLESHOOTING
500 Tennessee Waltz Parkway
Ashland City, TN 37015
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE AGENT.
PRINTED IN THE U.S.A 0510
318349-000
1

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Summary of Contents for A.O. Smith SERIES 120

  • Page 1 Service Handbook COMMERCIAL GAS WATER HEATERS MODEL BTR 500/A SERIES 120/121 INSTALLATION CONSIDERATIONS - PRE SERVICE INSTALLATION CONSIDERATIONS - PRE SERVICE CHECKS - OPERATION & SERVICE -TROUBLESHOOTING CHECKS - WATER HEATER CONSTRUCTION - OPERATION & SERVICE - TROUBLESHOOTING 500 Tennessee Waltz Parkway Ashland City, TN 37015 SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE AGENT.
  • Page 2: Table Of Contents

    COMMERCIAL GAS WATER HEATER SERVICE MANUAL TABLE OF CONTENTS INTRODUCTION ............3 Gas Control Valve/Burner Area View ......18 Qualifications ............3 Blower Prover Switch - Settings ......19 Service Warning............3 Thermostat and Ignition control Board View ...20 Service Reminder .............3 White Rodgers Integrated Control - Thermostat ..21 REQUIREMENTS ............4 White Rodgers Ignition Control Board ....21 Instruction Manual ............4...
  • Page 3: Introduction

    INTRODUCTION This Service Manual is designed to be an aid in servicing and troubleshooting A. O. Smith Master-Fit models BTR 500 Series 120/121 commercial water heaters. The instructions and illustrations contained in this service manual will provide you with troubleshooting procedures to verify proper operation and to diagnose and repair common service problems.
  • Page 4: Requirements

    REQUIREMENTS REQUIREMENTS INSTRUCTION MANUAL Have a copy of the instruction manual that came with the water heater on hand for the model being serviced. Instruction manuals can be obtained at the A. O. Smith web site (www.hotwater.com) or by calling technical support at 800 527-1953. Installation information given in this service manual is not a complete installation instruction.
  • Page 5: Installation Considerations

    INSTALLATION CONSIDERATIONS INSTALLATION CONSIDERATIONS Installation information given in this service manual IS NOT a complete installation instruction. Installation information covered in this service manual has a limited focus as it applies to servicing. This service manual does not replace or supersede the Instruction Manual that came with the water heater.
  • Page 6: Air Requirements

    INSTALLATION CONSIDERATIONS Table 1 NATURAL GAS PROPANE (LP) GAS 10” W.C. (2.49 kPa) 12” W.C. (2.99 kPa) ‡ Maximum Supply Gas Pressure † 5.2” W.C. (1.29 kPa) 11” W.C. (2.74 kPa) Minimum Supply Gas Pressure 3.5” W.C. (0.87 kPa) 10” W.C. (2.49 kPa) Manifold Gas Pressure ‡...
  • Page 7: Insufficient Make-Up Air, Negative Air Pressure, And Downdrafts

    INSTALLATION CONSIDERATIONS Insufficient Make-up Air, Negative Air Pressure, and Downdrafts A lack of combustion and ventilation air can create a negative ambient air pressure in the installed space. The vent system on one or more gas fired appliances can experience down drafts due to the outdoor air pressure being greater than the ambient air pressure in the installed space.
  • Page 8: Make-Up Air: Direct Communication With Outdoors

    INSTALLATION CONSIDERATIONS Make-up Air: Direct Communication with Outdoors A fresh supply of make-up air for combustion can be supplied to the water heater through make-up air ducts, which directly communicate with the outdoors. (Not Direct Vent.) Two openings are required: one within 12 inches of the top of the enclosure and one within 12 inches of the bottom of the enclosure.
  • Page 9: Contaminated Air

    INSTALLATION CONSIDERATIONS Contaminated Air Carefully review the warnings concerning contaminated combustion and ventilation air in the instruction manual that came with the water heater. Combustion air that is contaminated can greatly diminish the life span of the water heater and water heater components such as burners, igniters, flue baffles and vent system components.
  • Page 10: Clearances (Exterior)

    INSTALLATION CONSIDERATIONS Table 2 MINIMUM CLEARANCES TO COMBUSTIBLE SURFACES “A” - Right Side “B” - Left Side “C” - Back 5” (12.7 cm) 5” (12.7 cm) 5” (12.7 cm) A, B, and C clearances to non-combustible surfaces is “0” inches. A 20” clearance to cover remains unchanged. CLEARANCES (EXTERIOR) The illustration below shows the required clearances for venting units using natural draft venting.
  • Page 11: Venting

    INSTALLATION CONSIDERATIONS VENTING The BTR 500 water heater is classified by ANSI as a Category I (non-condensing, negative pressure venting) appliance. It is approved for type B vent. The blower (draft inducer) does not pressurize the exhaust. NOTE: This section of the service manual is not a complete venting installation instruction. Refer to the instruction manual that came with the water heater;...
  • Page 12: Operation And Service

    OPERATION AND SERVICE OPERATION AND SERVICE SEQUENCE OF OPERATION 1. Call for heat is activated when temperature sensed from Thermistor Probes falls below the Thermostat setting. 2. Blower (Draft Inducer) is energized. 3. Ignition Control Board verifies that the Blower Prover Switch is closed and that the Blower (Draft Inducer) is operating.
  • Page 13: Electrical Sequence

    OPERATION AND SERVICE ELECTRICAL SEQUENCE 1. Switch Power on to unit. 2. Thermostat calls for heat. 3. Ignition Control Board performs diagnostic check on system components. 4. On completion of diagnostics check, the Ignition Control Board energizes the Blower (Draft Inducer). 5.
  • Page 14: Wiring Diagram

    OPERATION AND SERVICE WIRING DIAGRAM INDUCER UPPER PROBE/ BLOWER PROVER PRESSURE SWITCH THERMOSTAT TO EARTH GROUND IGNITION BOARD 1a 1 1b HOT 120 VAC NEUTRAL EARTH GROUND LOWER PROBE NOTE: Must be properly grounded IGNITER/FLAME and have correct polarity SENSOR connections.
  • Page 15: Operating Sequence - Flow Chart

    OPERATION AND SERVICE OPERATING SEQUENCE - FLOW CHART Power On Call for Heat Control Locks Out - LED Self diagnostic check is performed Displays 2, 6, or 8 (Correct state of Blower Prover Switch and ECO is verified) Flash Error Code (polarity , earth ground , and Igniter presence are verified ) (See Error Code Chart ) Blower (Draft Inducer)
  • Page 16: Gas Control Valve

    OPERATION AND SERVICE GAS CONTROL VALVE This gas valve is a 24 volt AC combination-step opening valve. It includes two valves assembled in parallel, connected by a wiring harness. Note that the valves have fixed pressure regulation and are not adjustable. However, the manifold (outlet) pressure is adjustable as described on the next page.
  • Page 17: Manifold Pressure Adjustment

    OPERATION AND SERVICE Manifold Pressure Adjustment The main gas regulators are found beneath the silver or black cap screws. (Natural Gas valves have silver caps; Propane valves have a black caps). Remove the caps to access the outlet (manifold) pressure adjustment screw. IMPORTANT: Ensure that the outlet pressure matches the manifold pressure that is listed on the water heater rating plate.
  • Page 18: Gas Control Valve/Burner Area View

    OPERATION AND SERVICE GAS CONTROL VALVE/BURNER AREA VIEW Honeywell Gas Valve Rollout Shield Main Burner Shield Radiation Shield Main Burner with Hot Surface Igniter (HSI) mounted Figure 14 Table 3 HOT SURFACE IGNITER (HSI) Volts AC Nominal 80 VAC Ohms Resistance 11.0 - 20.0 @ 77°...
  • Page 19: Blower Prover Switch - Settings

    OPERATION AND SERVICE BLOWER PROVER SWITCH - SETTINGS Vent Connection Blower Prover Switch Exhaust/Outlet Optional Hot Water Outlet Blower (Draft Inducer) Figure 15 Table 4 BLOWER PROVER SWITCH TABLE BTR Model Pressure Setting to Close Switch (Inches W.C.) 500/A -2.85” ± 0.13” NOTE: The Blower Prover Switch contacts are normally open and will close on a fall in pressure.
  • Page 20: Thermostat And Ignition Control Board View

    OPERATION AND SERVICE THERMOSTAT AND IGNITION CONTROL BOARD VIEW Figure 16 Servicing should only be performed by a Qualifi ed Service Agent...
  • Page 21: White Rodgers Integrated Control - Thermostat

    OPERATION AND SERVICE WHITE RODGERS INTEGRATED CONTROL - THERMOSTAT Display LED Label Display Temperature LEDs Adjustment Dial To Upper Temp. Probe ECO Manual Reset Button To Ignition Control 120 VAC from Board Ignition Control Board To Lower Fuse Pin Number Temp.
  • Page 22: Pre-Service Checklist

    OPERATION AND SERVICE PRE-SERVICE CHECKLIST Use the following checklist BEFORE you begin servicing the water heater. 1. Have you removed the cover from the controls? • Did you take notice of the status lights on the upper water heater control? •...
  • Page 23: Troubleshooting

    TROUBLESHOOTING TROUBLESHOOTING IGNITION CONTROL BOARD: ERROR CODES The White Rodgers ignition control board will display a flashing error code with an LED light located on the upper left corner of the Ignition Control Board (Figure 18) when there is a problem. There is a distinctive pause between a series of on/ off flashes (1 to 8 flashes) when there is a problem.
  • Page 24: Flashes

    TROUBLESHOOTING 3 FLASHES Blower prover (air pressure) switch failed to close its normally open contacts after blower (draft inducer) was energized. Blower will run indefinitely, waiting for the blower prover switch circuit to close. Check air pressure reading at blower prover switch sensing port on blower fan housing with manometer (digital preferred);...
  • Page 25: Flashes

    TROUBLESHOOTING Check molex plug connector between igniter/flame sensor assembly and control board; Also check flame sense (12 pin) plug connection at control board. 8 FLASHES Igniter not sensed and/or water heater not grounded. Test igniter resistance. It should should be 11 - 20 ohms. Replace igniter if open continuity.
  • Page 26: Integrated Heater Control: Display Lights

    TROUBLESHOOTING INTEGRATED HEATER CONTROL: DISPLAY LIGHTS Power Energy Cut Off Status Call for Reset Heat Status INDICATION ACTION STATUS Calling for heat Normal status. No action required. • Check for excessively hot water The ECO (Energy Cut-Off) has (203° F or higher). opened.
  • Page 27: Test 1: 120 Vac To Heater Check

    TROUBLESHOOTING TEST 1: 120 VAC TO HEATER CHECK Conditions: • No Green Display “Power” LED on. • Plugs are in receptacles. • Supply power breaker is not open. • On/Off heater switch is on. White Rodgers White Rodgers Integrated Control Integrated Control t d C TO EARTH...
  • Page 28: Test 2: Polarity Check

    TROUBLESHOOTING TEST 2: POLARITY CHECK Conditions: • No hot water • Green “Power” LED is on. • Tank is more than 5° F below temperature dial setting. • Red ignition control board diagnostic LED is flashing 6 times between pauses. •...
  • Page 29: Test 3: Continuity Check Of High Limit (Eco)

    TROUBLESHOOTING TEST 3: CONTINUITY CHECK OF HIGH LIMIT (ECO) Conditions: • Power On – No Hot Water • Red, heater control “Call for Heat” LED – on • Red ignition control board diagnostic LED – 4 Flashes • Note LED Flash Code before resetting water heater control. •...
  • Page 30: Test 4: Upper Temperature Probe Continuity Check

    TROUBLESHOOTING TEST 4: UPPER TEMPERATURE PROBE CONTINUITY CHECK Conditions: • Power On - Water below temperature set point. • Red, water heater control “Reset Status” LED-OFF • “Call For Heat” LED off. Upper Temperature probe continuity check TEST 4 Red wire to red wire - Turn supply power “Off” for this test IF..
  • Page 31: Test 5: Calling For Heat - No Blower Operation

    TROUBLESHOOTING TEST 5: CALLING FOR HEAT - NO BLOWER OPERATION Conditions: • Power on • Plugs in Receptacles • Red “ Call for Heat” LED - ON • Blower (Draft Inducer) off Note flash code on ignition control board diagnostic LED. Water Heater Control - Thermostat “Call for Heat”...
  • Page 32: Test 6: Blower On, No Ignition

    TROUBLESHOOTING TEST 6: BLOWER ON, NO IGNITION Conditions: • Power on • Plugs in receptacles • Blower (Draft Inducer) operating • No power to Hot Surface Igniter (HSI). Note LED flash code. Blower Blower Exhaust Prover Switch Hot Water Outlet Blower (Draft Inducer) Check E4 pin 2 to ground...
  • Page 33: Test 7: Blower On, Blower Prover Switch Closed, No Igniter Operation

    TROUBLESHOOTING TEST 7: BLOWER ON, BLOWER PROVER SWITCH CLOSED, NO IGNITER OPERATION Conditions: • Power on, but no power to igniter • Plugs in receptacles • Blower (Draft Inducer) on • 24V at ignition board E1, Pin 10 Check E4 pin 4 to Ground Check E1 pin 10 - 24V Ground Continuity...
  • Page 34: Test 8: Igniter Heats, No Main Burner

    TROUBLESHOOTING TEST 8: IGNITER HEATS, NO MAIN BURNER 24 V. E1 Plug to Pin 9 E1 Plug to Pin 12 Figure 27 TEST 8 IGNITER HEATS..NO MAIN BURNER IF..then.... short heat up time of igniter check control box grounding. Normal warm up (Approximately 20 seconds) - check for 24V from E1, Pin 12 to ground during 4 second trial.
  • Page 35: Test 9: Igniter Heats, No Main Burner

    TROUBLESHOOTING TEST 9: IGNITER HEATS, NO MAIN BURNER Conditions: • Test 8 completed • Turn off power • Disconnect wires from gas valve Inlet Manifold Manifold Pressure Pressure Measure Resistance Between Gas Valve Terminals (Main Valve Solenoid Connections) Outlet Figure 28 TEST 9 IGNITER HEATS –...
  • Page 36: Test 10: Main Burner Ignition For Less Than Five Seconds

    TROUBLESHOOTING TEST 10: MAIN BURNER IGNITION FOR LESS THAN FIVE SECONDS Conditions: • Power On; plug connected • Main Burner ignites for approximately five seconds, then goes out. • Tests 8 and 9 completed Note the flash code on the ignition board LED. Hot Surface Igniter (HSI) HSI Mounted on Main Burner E1, Pin 2 (From Flame Proving Rod)
  • Page 37: Test 11: Water Heater Shutting Off Below Setting

    TROUBLESHOOTING TEST 11: WATER HEATER SHUTTING OFF BELOW SETTING Conditions: • Main burner ignited • Stored water is below temperature setting more than 5° F (Tank Average). • Power off • Plug disconnected from heater control board receptacle E3 and E4 Figure 30 WATER HEATER SHUTTING OFF BELOW SETTING TEST 11...
  • Page 38 NOTES Servicing should only be performed by a Qualifi ed Service Agent...
  • Page 39 NOTES Servicing should only be performed by a Qualifi ed Service Agent...
  • Page 40 500 Tennessee Waltz Parkway, Ashland City, TN 37015 Technical Support: 800-527-1953 • Parts: 800-433-2545 • Fax: 800-644-9306 www.hotwater.com Copyright © 2010 A.O. Smith Corporation. All rights reserved.

This manual is also suitable for:

Btr 500/aSeries 121

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