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Service Handbook
COMMERCIAL GAS HIGH EFFICIENCY WATER HEATERS
FOR MODELS:
BTH 120 THRU 500
SERIES 200/201
INSTALLATION CONSIDERATIONS - PRE SERVICE CHECKS -
500 Tennessee Waltz Parkway
CONSTRUCTION - OPERATION & SERVICE - TROUBLESHOOTING
Ashland City, TN 37015
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE TECHNICIAN
PRINTED IN THE U.S.A. 0914
329297-000
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Table of Contents
Related Manuals for A.O. Smith BTH 120
Summary of Contents for A.O. Smith BTH 120
- Page 1 Service Handbook COMMERCIAL GAS HIGH EFFICIENCY WATER HEATERS FOR MODELS: BTH 120 THRU 500 SERIES 200/201 INSTALLATION CONSIDERATIONS - PRE SERVICE CHECKS - 500 Tennessee Waltz Parkway CONSTRUCTION - OPERATION & SERVICE - TROUBLESHOOTING Ashland City, TN 37015 SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE TECHNICIAN PRINTED IN THE U.S.A.
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Page 2: Table Of Contents
Modulation ..................38 Combustion Blower & Burner Assembly ..........4 BLOWER SPEED CONTROL – BTH 300 THRU 500 ......40 Top View: BTH 120 - 250 Models ............5 VARIABLE FREQUENCY DRIVE – BTH 300 THRU 500......41 Top View: BTH 300 - 500 Models ............5 BURNER ASSEMBLY ................42... -
Page 3: Introduction
INTRODUCTION This Service Handbook covers the water heater Model and Series numbers listed on the front cover only. The instructions and illustrations contained in this service handbook will provide you with troubleshooting procedures to verify proper operation and diagnose and repair common service problems. QUALIFICATIONS QUALIFIED INSTALLER OR SERVICE AGENCY Installation and service of this water heater requires ability equivalent to that of a Qualified Agency (as defined... -
Page 4: Installation Considerations
INSTALLATION CONSIDERATIONS This section of the Service Handbook covers some of the critical installation requirements that, when overlooked, often result in operational problems, down time and needless parts replacement. Costs to correct installation errors are not covered under the limited warranty. Ensure all installation requirements and instructions contained in the Instruction Manual that came with the water heater have been followed prior to performing any service procedures. -
Page 5: Features And Components
Sight Glass Gasket Burner Plate Burner Plate Gasket (150-250 Models Only) SS Heat Shield (150-250 Models Only) Flue Ring Gasket BTH 120 - 250 Models Ignition Cable Spark Igniter Flame Sensor Spark Igniter Gasket Air Intake Assembly Combustion Blower Blower Gasket... -
Page 6: Top View: Bth 120 - 250 Models
TOP VIEW: BTH 120 - 250 MODELS Junction Box Assembly Powered Anode (Short, BTH 150-250 Models Only) Burner/ Blower Assembly Ignition Control Powered Anode (Long) Blower Prover Switch (Label Color: Green) CCB Assembly Blocked Air Intake Switch (Label Color: Blue) -
Page 7: Sequence Of Operation Flow Chart
SEQUENCE OF OPERATION FLOW CHART Sequence is shown with Enable/Disable Switch in the Enable position If tank temperature drops below Operating Set Point minus Differential setting a heating cycle is activated Control System performs diagnostic checks Normal State of all pressure switches and ECO are checked Control System Locks Out Blower Prover pressure switch verified open Displays Fault Msg... -
Page 8: Fault And Warning Codes
FAULT AND WARNING CODES 1. LOW GAS PRESSURE CAUSES: Low Gas Pressure • The Low Gas Pressure Switch is detecting gas Fault occurred 2 mins ago pressure below the value required for proper Gas pressure is below minimum operation. required to operate this unit. Check gas pressure and switch. -
Page 9: Gas Supply Systems
14" W.C. under any upstream supply pressure or condition. For Natural Gas BTH 120-250 models require a minimum gas supply pressure of 4.4" W.C., BTH 300-500 models require 4.8" W.C., and all models require 8.5" W.C. for propane gas. The minimum supply pressure is measured while gas is flowing (dynamic pressure) along with all additional gas appliances operating on the same gas supply system. -
Page 10: Gas Pressure Test
GAS CONTROL VALVE COMBUSTION BLOWER CONNECTION COMBUSTION AIR INLET MANIFOLD GAS SUPPLY GAS VENTURI PRESSURE PRESSURE TEST PORT TEST PORT BTH 120 - 250 Models BTH 300 - 500 Models Servicing should only be performed by a Qualified Service Technician... - Page 11 7. Record the supply gas pressure. 8. Use the Enable/Disable Switch located on the front of the water heater and put the unit in enabled mode. The settings on the water heater may need to be changed to cause the water heater to operate. Note the Operating Temperature Set Point so that the unit can be returned to this setting at the conclusion of this test procedure.
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Page 12: Blower Operation Error
2. BLOWER OPERATION ERROR CAUSES: Blower Operation Error • The Blower Prover Pressure Switch was detected closed before blower operation. Fault occurred 2 mins ago Blower Prover Pressure Switch may have failed closed. Check/replace pressure switch. Call a service professional: Your Company Name Here (press [DOWN] for more..) CHANGE... -
Page 13: Pressure Switch Tests
PRESSURE SWITCH TESTS Complete pressure switch testing involves three procedures: • "Continuity Test During Standby" below. • "Continuity Test During Operation" on Page 13. • "Pressure Test During Operation" on Page 13 thru Page 15. CONTINUITY TEST DURING STANDBY This test is performed while the Combustion Blower is not running with the water heater turned off. This is a "normal state"... -
Page 14: Continuity Test During Operation
CONTINUITY TEST DURING OPERATION This test is performed while the Combustion Blower is running at high speed during the Pre-Purge operating state. The test is performed on all three pressure switches. Disconnect the two wires to each pressure switch - one at a time, check continuity and then reconnect the wires to that switch before testing the next switch. 1. -
Page 15: Pressure Switch Settings
Blocked Air Blocked Exhaust Low gas (+/-0.04" WC Nat/ (+/- 0.05" WC) Intake (+/-0.05" WC) +/-0.05" WC LP) (+/-0.05" WC) BTH 120 0.75" W.C. -2.50" W.C. 2.00" W.C. 4.4" W.C. Nat/8.5" W.C. LP BTH 150-250 1.00" W.C. -2.50" W.C. 2.00" W.C. - Page 16 the water heater's rating label) for the water heater being serviced on hand before calling. Blocked Air Intake: Note these are negative pressures; in a vacuum. If the pressure reading taken at the Blocked Air Intake Switch sensing tube does not reach or drop lower than the pressure shown in the above Table AND the switch contacts were opening during the "Continuity Test During Operation"...
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Page 17: Blower Prover Open
3. BLOWER PROVER OPEN CAUSES: Blower Prover Open • The control has detected an open Blower Prover Fault occurred 2 mins ago Pressure Switch during operation. The blower prover switch remains • Blower Prover Pressure Switch sensing tube open after the blower has been disconnected or kinked. -
Page 18: Ignition Failure
4. IGNITION FAILURE CAUSES: Ignition Failure • On an “Ignition Failure” error, either the burner is Fault occurred 2 mins ago not igniting or the burner is igniting, but the Flame Flame not detected. Clean flame rod. Sensor is not detecting ignition (flame). Check gas supply. - Page 19 SUPPLY GAS VALVE CONNECTION LOW GAS PRESSURE SWITCH COMBUSTION AIR INLET VENTURI GAS CONTROL VALVE ASSEMBLY: BTH 120 - 250 MODELS SUPPLY GAS CONNECTION LOW GAS PRESSURE SWITCH 24 VAC SOLENOID & WIRE HARNESS GAS CONTROL VALVE ASSEMBLY: BTH 300 - 500 MODELS...
- Page 20 • Remove and reinsert the circuit board end of the Gas Control Valve connector. Make sure it is connected tightly and that the pins are clean. • Recycle unit again to start another ignition cycle. If you still do not see a brief blue flame through the sight glass at the moment the Gas Control Valve icon appears on the display, verify that 24 VDC is present on the connector pins 1 and 5.
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Page 21: Blocked Air Intake
5. BLOCKED AIR INTAKE CAUSES: Blocked Air Intake • The Blocked Air Intake Switch has detected a Fault occurred 2 mins ago possible restriction in the air intake pipe. Restriction in air intake. Check intake pipe and termination for blockage. Call a service professional: Your Company Name Here (press [DOWN] for more..) -
Page 22: Blocked Exhaust
6. BLOCKED EXHAUST CAUSES: Blocked Exhaust • The Blocked Exhaust Switch has detected a possible restriction in the exhaust pipe. Fault occurred 2 mins ago Restriction in exhaust pipe. Check exhaust pipe and termination for blockage. Call a service professional: Your Company Name Here (press [DOWN] for more..) CHANGE... -
Page 23: Flame Sensor Error
Volt Gas Control valve wiring harness, see Figures below. 24 VAC SOLENOID & WIRE HARNESS GAS CONTROL SUPPLY GAS VALVE CONNECTION LOW GAS PRESSURE SWITCH COMBUSTION AIR INLET VENTURI GAS CONTROL VALVE ASSEMBLY: BTH 120 - 250 MODELS Servicing should only be performed by a Qualified Service Technician... -
Page 24: Gas Control Valve Voltage Tests
SUPPLY GAS CONNECTION LOW GAS PRESSURE SWITCH 24 VAC SOLENOID & WIRE HARNESS GAS CONTROL VALVE ASSEMBLY: BTH 300 - 500 MODELS GAS CONTROL VALVE VOLTAGE TESTS 1. The animated Gas Control Valve Status Icon is displayed on the Control System UIM during these operating states. -
Page 25: Flame Sensor
FLAME SENSOR Ignition of the Burner is controlled electronically. The principle of operation for electronic ignition relies on flame sensing current to prove the fuel gas flowing to the Burner has been ignited. Flame sensing requires an adequate earth ground to the water heater's Burner, see "Electrical Connections" on Page 35. -
Page 26: Flame Sensing Current Test
FLAME SENSING CURRENT TEST During the heating cycle the flame sensing current is normally greater than 8.0 μA with a clean Flame Sensor. Over time the Flame Sensor can degrade and this will reduce flame sensing current. With heavier use, more heating cycles/greater load, this will occur more quickly. -
Page 27: No Water
CHECK/ REPAIR: POWERED ANODES The water heaters covered by this Service Handbook are equipped with powered anodes. BTH 120 models only use 1 powered anode, all others will have two. These anodes do not need to be replaced unless damaged. The CCB monitors the current through the anodes and will declare a fault if there is a disconnected wire or if there is no water in the tank. - Page 28 CLEANING METHOD: If corrosion is present on the air side of the anode, use a wire brush to clean the outer nut and brass wire terminal tab. To clean the inner nut, remove the outer nut and the brass wire terminal tab. DO NOT REMOVE inner nut.
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Page 29: Anode Shorted
9. ANODE SHORTED CAUSES: Alert: • The controller has detected a low resistance or Anode Shorted short to earth ground or the tank. Alert occurred 0 mins ago The Powered Anode is shorted to earth ground or the tank. Note: This is an alert. The unit will continue to heat water in (press [DOWN] for more..) CHANGE... -
Page 30: Temperature Probe Short (Upper Or Lower)
10. TEMPERATURE PROBE SHORT (UPPER OR LOWER) CAUSES: Upper Temp Probe (Short) • The Upper or Lower Temperature Probe appears Fault occurred 0 mins ago to be shorted (very low resistance). This fault code Upper Temperature Probe may be shorted. Check connector and often means the connector has been corroded by resistance of Probe. -
Page 31: Temperature Sensor Test
If the resistance of the Temperature Sensor is below 390 ohms the Control System will lock out and display Temp Probe Short on the UIM. If the resistance of the temperature sensor is above 56,000 ohms the Control System will lock out and display Temp Probe Open on the UIM. The electrical circuit breaker that serves the water heater must be turned off and on again to reset the Control System. - Page 32 Results/Actions • If the ohm meter shows continuity (closed circuit) between the two outside pins (red wires) the ECO switch has reset properly. If the Control System continues to lock out displaying Energy Cut Out (ECO) on the UIM with continuity through the ECO present call the toll free support phone number listed on the back cover of this manual for further assistance.
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Page 33: Temperature Probe Open (Upper Or Lower)
11. TEMPERATURE PROBE OPEN (UPPER OR LOWER) CAUSES: Lower Temp Probe (Open) • The Upper or Lower Temperature Probe appears Fault occurred 0 mins ago to be open (very high resistance). This fault code Lower Temperature Probe may be often means the connector has been corroded by open. -
Page 34: Venting
VENTING This section of the Service Handbook is not a complete venting installation instruction. Refer to the Instruction Manual that came with the water heater; ensure the venting has been installed per all Instruction Manual requirements. Costs to correct installation errors are not covered under the limited warranty. GENERAL VENTING INFORMATION The water heaters covered in this Service Handbook are operationally equivalent to Category IV appliances and may be installed in either a Power Vent or Direct Vent configuration. -
Page 35: Intake Air Connection
4” x 3” REDUCER COUPLING - FACTORY INSTALLED INTAKE AIR CONNECTION DETAIL INTAKE AIR CONNECTION DETAIL BTH 120 - 250 Models BTH 300 - 500 Models AIR INTAKE SCREEN Service Notes: • Plastic debris left on the edges of intake air pipe sections after cutting must be removed on Direct Vent installations. -
Page 36: Electrical Connections - All Models
ELECTRICAL CONNECTIONS – ALL MODELS The water heaters covered in this Service Handbook require a 120 VAC, 1Ø (single phase), 60Hz, 15 amp power supply and must also be electrically grounded in accordance with local codes or, in the absence of local codes, with the National Electrical Code, ANSI/NFPA 70 or the Canadian Electrical Code, CSA C22.1. -
Page 37: Enable/ Disable Switch
5. Connect the ground wire from the power supply to the grounding lug inside the junction box. See Junction Box Assembly Figure below and "Wiring Diagrams" on Page 52 & Page 53. 6. Replace junction box cover when connections are complete. Note: Do not apply power to the water heater before installation is complete and the water heater is filled with water. -
Page 38: Installation Check List
INSTALLATION CHECK LIST The list below represents some of the most critical installation requirements that, when overlooked, often result in operational problems, down time and needless parts replacement. Before performing any troubleshooting procedures use the list below to check for installation errors. Costs to correct installation errors are not covered under the limited warranty. -
Page 39: Operation And Service
3 pin wiring plug receiving 120 VAC from the Junction Box. The CCB sends a signal from the J5 socket to a 5 pin wiring socket on the BTH 120-250 blower and VFD on the BTH 300-500 top cover control assembly. The signal is an electronic instruction to start, stop and control blower speed. - Page 40 The 5 pin PWM signal plug MUST remain plugged in to the 5 pin socket on the blower assembly at all times (BTH 120-250 Models only). Disconnecting this plug will cause the Combustion Blower to stop. If the electronic speed control is functioning properly Combustion Blower speed should noticeably reduce during the Trial For Ignition operating state.
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Page 41: Blower Speed Control - Bth 300 Thru 500
BLOWER SPEED CONTROL – BTH 300 THRU 500 The CCB monitors a feedback signal from a sensor that is installed on the blower. The CCB interprets the pulse signal from the sensor and then sends a signal to the variable frequency drive (VFD) which in turn transmits the proper frequency to the blower to produce the proper blower speed and input. -
Page 42: Variable Frequency Drive - Bth 300 Thru 500
VARIABLE FREQUENCY DRIVE – BTH 300 THRU 500 The BTH 300 - 500 models have a variable frequency drive (VFD) that controls the rpm of the blower motor. The VFD receives a signal from the central control board that instructs the VFD to transmit the proper frequency to the blower to produce the proper blower speed and proper input. -
Page 43: Burner Assembly
See the exploded view of the "Combustion Blower & Burner Assembly" section on Page 4 also. BTH 120 - 250 Models BTH 300 - 500 Models Servicing should only be performed by a Qualified Service Technician... -
Page 44: Combustion Blower And Burner Removal/ Installation Instructions
10. Disconnect the Blower Prover Switch sensing tube (light blue soft tubing) from the Combustion Blower outlet sensing port. 11. Using a socket wrench with a ½” deep well socket remove the four (BTH 120), six (BTH 150-250), or eight (BTH 300-500) ½” nuts from the studs holding the burner plate in place. -
Page 45: Spark Igniter
Spark Igniter (1/8" Spark Igniter Spark Gap) (5/16" Gap from Burner) Flame Sensor (1/2" Gap from Burner) BTH 120 - 250 Models Servicing should only be performed by a Qualified Service Technician... - Page 46 Spark Igniter (1/8" Spark Igniter Spark Gap) (5/16" Gap from Burner) Flame Sensor (13/16" Gap from Burner at the tip of Sensor Rod) BTH 300 - 500 Models The Control System is programmed to start sparking a few seconds before the Gas Control Valve opens. See the "Sequence Of Operation Flow Chart"...
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Page 47: Gas Orifice - Bth 300 Thru 500 Models
GAS ORIFICE - BTH 300 THRU 500 MODELS Refer to Orifice Chart below for correct gas orifice size. BTH 120 thru 250 Models and all Natural gas models do not use a gas orifice. w/LP Gas Orifice Without Orifice Gas Control Without Orifice Natural Gas... -
Page 48: Ccb (Central Control Board)
CCB (CENTRAL CONTROL BOARD) The CCB is a printed circuit board mounted inside a protective plastic enclosure, see Figures below and on next page. The CCB circuit board is the main control. All instructions for ignition and temperature control originate from this circuit board. Diagnostic and operational messages are generated by the CCB and sent to the UIM, see "(UIM) User Interface Module Screen"... -
Page 49: Ccb Cover Removal And Replacement
CCB COVER REMOVAL AND REPLACEMENT The cover on the CCB enclosure must be removed for various service procedures outlined in this Service Handbook. Refer to the instructions below when removing and replacing the CCB cover. Wiring to and from the CCB and other water heater components enters the CCB enclosure on the bottom. Removing the enclosure cover is a simple procedure. -
Page 50: Ccb Circuit Board Layout
CCB CIRCUIT BOARD LAYOUT CCB (CENTRAL CONTROL BOARD) POWER BOARD ASSEMBLY Servicing should only be performed by a Qualified Service Technician... -
Page 51: Ccb Connection Identification
CCB CONNECTION IDENTIFICATION J1 Socket - High Voltage In PIN # DESCRIPTION Ground AUX NC AUX NO AUX Common Not Used AUX NO AUX Common Line Voltage Neutral J5 Socket - Blower Logic (VFD/ Blower) PIN # DESCRIPTION PWM Signal Not used Blower Speed Feedback Grounding... - Page 52 J14 Socket - Limit String PIN # DESCRIPTION Anode Grounding Flame Sensor Condensate Not Used Condensate Gas Pressure Switch Gas Pressure Switch Gas Control Valve Gas Control Valve 24V Return J15 Socket - Pressure Switches PIN # DESCRIPTION Blower Prover Pressure Switch / Blocked Air Intake Pressure Switch Blocked Air Intake Pressure Switch / Blocked Exhaust Pressure Switch Blower Prover Pressure Switch Blocked Exhaust Pressure Switch...
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Page 53: Wiring Diagram - Bth 120 Thru 250
WIRING DIAGRAM – BTH 120 THRU 250 Servicing should only be performed by a Qualified Service Technician... -
Page 54: Wiring Diagram - Bth 300 Thru 500
WIRING DIAGRAM – BTH 300 THRU 500 Servicing should only be performed by a Qualified Service Technician... -
Page 55: Control Overview
CONTROL OVERVIEW Interaction with the water heater controller is through an UIM display called the User Interface Module (UIM). This screen is also referred to as the “desktop” or “desktop menu”. Up and down buttons and three operation buttons allow navigation through the control menus and to make adjustments to the water heater. - Page 56 COMMERCIAL GAS HIGH EFFICIENCY WATER HEATERS For additional information contact: A. O. Smith Corporation 500 Tennessee Waltz Parkway Ashland City, TN 37015 Tech Support: 800-527-1953 Parts: 800-433-2545 www.hotwater.com Copyright © 2014 A. O. Smith Water Heater Company, All rights reserved.