Related Manuals for A.O. Smith VF VB 1000
Summary of Contents for A.O. Smith VF VB 1000
- Page 1 Variable Fire Boiler Domestic Hot Water/Hydronic Heating M O D E L S C O V E R E D VW and VB 500, 750, and 1000 Models Series 100 and 101 Part No. TC-099 • Printed in the U.S.A. • 0407...
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Page 2: Table Of Contents
A. O. SMITH WATER PRODUCTS COMPANY Introduction... Qualifications... Service Warning... Tools Required... EMC 5000 Modulation Control System... UIM - User Interface Module - Overview... UIM - Status Lights... UIM - Input Buttons... UIM - Changing Settings... UIM - Menu Screens... Principles of Operation... -
Page 3: Introduction
INTRODUCTION This Service Manual is designed to aid in servicing and troubleshooting A. O. Smith VF boilers. Models VW/VB 500 - 1000 - series 100/101 boilers are covered in this manual. The instructions and illustrations contained in this service manual will provide you with troubleshooting procedures to verify proper operation and diagnose and repair common service problems. -
Page 4: Tools Required
Tools Required • Instruction Manual that came with the boiler. • Hand tools common to installation and service of commercial water heaters and boilers. • TORX® T40 or 5mm hex wrench - for setting gas mixture at gas valve. • 3mm or 7/64in hex (allen) wrench - for setting gas mixture at gas valve. •... -
Page 5: Emc 5000 Modulation Control System
EMC 5000 MODULATION CONTROL SYSTEM This portion of the service manual will cover the EMC 5000 Modulation Control system (EMC - Energy Management Control). The EMC 5000 control system includes several components: a UIM (User Interface Module), a MCB (Modulation Control Board), and a PDB (Power Distribution Board). - Page 6 UIM - USER INTERFACE MODULE - OVERVIEW The UIM is an assembly that consists of several electronic components. The main circuit board in the assembly is the UIB (User Interface Board) which houses the communications port. The UIB relays user input and data to and from the MCB, controls the LCD, and activates the LEDs.
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Page 7: Uim - Status Lights
UIM - USER INTERFACE MODULE - STATUS LIGHTS LCD display 4 line x 20 character Soft lock-outs will automatically reset after the condition that caused the error has been corrected or a factory programmed time period of one hour. Soft lock-outs can also be reset by touching the Select button while the error screen is displayed. -
Page 8: Uim - Input Buttons
UIM - USER INTERFACE MODULE - USER INPUT BUTTONS LCD display 4 line x 20 character Select Button is used to: • Enter menu screens. • Activate adjustment mode for various settings. The [ > ] will be flashing slowly to the left of the menu item when the adjustment mode is active. •... -
Page 9: Uim - Changing Settings
UIM - USER INTERFACE MODULE - CHANGING SETTINGS The sequence of UIM screen displays below is an example of how to navigate the menus to change the Operating Set Point. Screen Display 1: shows the temperatures screen. This is the default display screen the UIM comes to rest at after approximately 60 seconds without any user input. -
Page 10: Uim - Menu Screens
UIM - USER INTERFACE MODULE - MENU SCREENS At the top center of the UIM panel is the display LCD. This LCD is used to provide information to the user through menu activated screens. Within each of the screens, helpful context sensitive information can be displayed at any time by touching the “Help”... - Page 11 UIM - USER INTERFACE MODULE - MENUS Log & System Info Screen: This screen displays the following: • Elapsed hours of operation (Total time system has been powered up). • Number of running minutes (Number of minutes system has been in the run mode). •...
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Page 12: Principles Of Operation
PRINCIPLES OF OPERATION VF boilers do not have a gas orifice. The blower “pulls” gas from the gas valve into a Venturi attached to the suction (inlet) side of the blower (page 12). As the speed of the blower is increased the vacuum in the Venturi is also increased and more fuel gas and combustion air is supplied to the burner. -
Page 13: Venturi Operation - Gas Train
PRINCIPLE OF OPERATION (CONT) Venturi Operation - Gas Train A Venturi is connected to the inlet side of the combustion blower on VF Boilers. The gas line from the outlet of the gas valve connects to the Venturi. The Venturi contains a cone shaped restrictor that constricts the air passage to the blower. -
Page 14: Blower Speed Verification - Hall Effect Sensor
PRINCIPLE OF OPERATION (CONT) Blower Speed Verification - Hall Effect Sensor The MCB (page 25) initiates blower operation by closing the VFD enable/disable circuit AND sending a 1-10 VDC speed instruction to the VFD (page 11) to energize the blower and to modulate blower speed. -
Page 15: Config Key - Blower Speed Programming
PRINCIPLE OF OPERATION (CONT) Config Key - Blower Speed Programming The Config Key is an 18” long cable with a plug on one end and an EEPROM memory chip sealed at the other. The Config Key plugs into the J23 socket on the MCB Daughter Board (see pages 25 and 34). -
Page 16: Sequence Of Operation
SEQUENCE OF OPERATION EMC 5000 Control System compares the temperature read from controlling probe (Inlet or remote Tank/Loop) to the Operating Set Point. If the temperature read is less than the Operating Set Point minus Stage 1 Differential AND the Enable/Disable (thermostat) circuit is closed a call for heat is activated Boiler enters Service Mode... - Page 17 SEQUENCE OF OPERATION (CONT) NOTE The events shown in this flow chart are in sequential order. The EMC 5000 is a multi-task control that performs some functions simultaneously. Only key events are shown in order to provide a general understanding of how the control operates.
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Page 18: Start Up Procedure
START UP PROCEDURE Prior To Start Up In addition to normal supplies and hand tools necessary for installing and servicing water heaters and boilers the following tools and test equipment should be on hand. See the tool requirements page 3. •... - Page 19 START UP PROCEDURE (CONT) Start Up Procedure 1. Before starting the boiler, please review the boilers Instruction Manual supplied with the boiler. Ensure the water piping, gas line, controls, and venting have been installed per the instruction manual. Further information on water piping and controls is on pages 61 - 67 in this service manual.
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Page 20: Adjusting Manifold Gas
START UP PROCEDURE (CONT) Adjusting Manifold Gas 13. Set the boiler to Max Mode (Firing Modes - page 17). Check combustion readings using combustion analyzer. Compare CO combustion readings are not in accordance with the high fire CO follows: Remove the flat, round, blue plastic cap from the top of the boiler’s 24 VAC gas valve. Using a 3mm (7/64”) hex wrench, turn the high fire adjustment screw under the cap counterclockwise to increase or clockwise to decrease gas flow and achieve the desired level per high fire table below. -
Page 21: Poor Combustion - Ignition Problems
POOR COMBUSTION - IGNITION PROBLEMS If the high and/or low fire CO shown on page 19, the CO readings are high, or if the boiler is experiencing ignition failure or rough starting perform the following procedures: Adequate Combustion - Proper Venting 1. - Page 22 POOR COMBUSTION - IGNITION PROBLEMS (CONT) Burner Inspection 2. Remove the burner and inspect the burner for any signs of damage or debris inside. If the burner is damaged or contaminated with debris - replace the burner. Check all gaskets in the burner/blower assembly for wear or damage. Replace any worn or damaged gaskets.
- Page 23 POOR COMBUSTION - IGNITION PROBLEMS (CONT) VFD Operating Parameters Approximate MCB/VFD operating parameters for natural gas models are shown in the first table below. Parameters for propane models are shown in the second table. When combustion is poor, the firing rate of the boiler or blower speed is in question, or the boiler is experiencing rough starts or ignition failure compare the values given here to actual readings taken during the various operating states shown.
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Page 24: Manifold Gas Pressure Check
POOR COMBUSTION - IGNITION PROBLEMS (CONT) Manifold Gas Pressure Check 5. Attach Digital manometer to one of the manifold gas pressure taps on gas line between the boiler’s 24 VAC gas valve outlet and the gas inlet on the Venturi as shown in the images below. -
Page 25: Control Panel Layout
CONTROL PANEL LAYOUT The illustration below shows the control panel on VF boilers. Blower Prover Switches VF boilers are equipped with High and Low blower prover switches or BPS. Both are normally open air pressure switches. Both close on a fall in pressure (a negative/vacuum pressure). -
Page 26: Mcb - Modulation Control Board
MCB - MODULATING CONTROL BOARD - OVERVIEW MCB / CCB / FCB Terminology Explanation MCB and CCB are separate terms that refer to the same circuit board which is the main controller for the EMC 5000 control system on VF boilers. MCB stands for “modulating control board,”... - Page 27 MCB - MODULATING CONTROL BOARD - OVERVIEW (CONT) The MCB circuit board is the main controller. All instructions for burner modulation and temperature control originate from this circuit board. Diagnostic and operational messages are generated by the MCB and sent to the UIM. Most of the boiler’s components, such as the igniter, blower, gas valve, and temperature probes are directly connected to one of the MCB’s 16 socket connectors.
- Page 28 MCB - SECTION A The upper left corner of the MCB contains the following sockets/components: Red LED (illuminated when the F1 fuse is open or missing) F1 Fuse (7.5 amp automotive fuse - 24 VAC transformer protection) J3 Socket (24 VAC power supply from transformer) •...
- Page 29 MCB - SECTION B The upper middle section of the MCB contains the following sockets/components: † J4 Socket (Outputs/Inputs) • Pin 1 - Spare - not used • Pin 2 - Spare - not used • Pin 3 - Spare - not used •...
- Page 30 MCB - SECTION C The upper right corner of the MCB contains the following sockets/components: J2 Socket (Pump relay coil; IRI gas valve) • Pin 1 - 120 VAC switched hot wire to pump relay coil • Pin 2 - 120 VAC neutral wire to pump relay coil •...
- Page 31 MCB - SECTION D MCB Master Control Dip Switches System configurations are made on the MCB circuit boards with dip switches. This page explains how the Master Control dip switches (SW1) are configured on the MCB. These dip switch/configuration settings can be viewed from the “Configuration Settings” menu screen on the UIM (see page 9).
- Page 32 MCB - SECTION E The lower left corner of the MCB contains the following sockets/components: J6 Socket (Gas valve relay - N/A on VF boilers) • Pin 1 - 24 VDC gas valve relay circuit • Pin 2 - N/A - plug is filled •...
- Page 33 VF BOILER SERVICE MANUAL MCB - SECTION F This section of the MCB contains the communication or “Comm” ports: ICSP Port The ICSP port (In Circuit Serial Programming) is used for programming the MCB board. DO NOT plug any device or cable into this port. This port is used by A. O. Smith engineering personnel only. Damage caused by plugging cables/devices into this port would not be covered under warranty.
- Page 34 MCB - SECTION G Along the bottom edge of the MCB there is a second dip switch (SW2). This page details and explains the SW2 dip switch. There are 3 switches on SW2: switch 1 is a spare, switch 2 must be configured correctly, dip switch 3 does not affect operation on VF boilers. Switch 1 Spare High gas pressure switch present On = Yes...
- Page 35 MCB SECTION H This section of the MCB contains a small “Daughter Board” that contains the J23 and J24 sockets. Refer to page 25 for more information. The VFD (page 11), the Hall Effect sensor (page 13) and the Config Key (page 14) connect to this Daughter Board. Service Notes: J24 Pins 1 and 2 (1-10 VDC VFD instruction) are polarity sensitive.
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Page 36: Pdb - Power Distribution Board
VF BOILER SERVICE MANUAL PDB - POWER DISTRIBUTION BOARD - OVERVIEW The PDB provides connection points for line-input (120 VAC) power, the pump, and the transformer. It distributes the line-input power and the transformer output (24 VAC) power to necessary locations. It also contains fuses for the pump and the MCB circuit board. The PDB also contains filtering circuitry for EMI/RFI (page 4) power supply protection. - Page 37 PDB - SECTION A The left side of the PDB circuit board contains a terminal strip (TB1) used to connect the 120 VAC power supply to the boiler, the pump relay, and the pump motor. VW models will have a factory mounted pump powered by the pump relay;...
- Page 38 PDB - SECTION B The mid section of the PDB contains the fusing for the following: F1 Fuse - 10 amp 240 VAC - European Models only † F2 Fuse - 20 amp 120 VAC - Pump F3 Fuse - 3 amp 120 VAC - Transformer Primary Winding F4 Fuse - 10 amp 120 VAC - FCB 4 Power Supply - N/A on VF boilers F5 Fuse - 10 amp 120 VAC - FCB 3 Power Supply - N/A on VF boilers F6 Fuse - 10 amp 120 VAC - FCB 2 Power Supply - N/A on VF boilers...
- Page 39 PDB - SECTION C The upper right corner of the PDB contains the following: J2 Socket (24 VAC Outputs) • Pin 1 - 24 VAC Hot to MCB J3 Socket • Pin 2 - 24 VAC Return to MCB J3 Socket •...
- Page 40 PDB - SECTION D The lower right corner of the PDB contains the J3 Socket and the JP1 jumper. The J3 Socket is described here the JP1 jumper is described on page 40. J3 Socket (120 VAC Outputs) • Pin 1 - 120 VAC Hot to MCB J1 Socket •...
- Page 41 PDB - POWER SUPPLY TEST The lower right corner of the PDB also contains two jumpers and three power supply status LED lights. With power applied the green DS2 LED should always be lit. The JP1 jumper is used to activate a power supply test function. The JP2 and JP3 jumpers are used for manufacturing purposes only.
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Page 42: Troubleshooting - Error Messages
ERROR MESSAGES - TROUBLESHOOTING The EMC 5000 control system performs exhaustive self diagnostics and displays detected fault conditions on the UIM (page 6). There are approximately 80 different error messages. Troubleshooting procedures for the most common error messages are covered in this service manual. -
Page 43: Display Is Blank
ERROR MESSAGES DISPLAYED MESSAGE CONDITION/INDICATES UIM Display Is Blank Boiler is turned off 120 VAC power supply problems 24 VAC power supply problems Blown Fuses Defective transformer Wiring or plug/socket connection problems UIM communication cable problems Important Service Reminder: When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. -
Page 44: Error Message "Display Fail
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Display Fail” Communication between the MCB and UIM has been interrupted - the MCB is having trouble communicating with the UIM. Important Service Reminder: When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. -
Page 45: Error Message "Config Key Crc
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Config Key CRC” Data read from the Config Key by the MCB was not properly confirmed at power up. The Config Key contains model specific (Btu/hr & fuel type) blower speed programing data. This data is written to the MCB’s internal memory at power up. -
Page 46: Error Message "Low Ac Voltage
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Low AC Voltage” Power supply polarity is reversed. Line voltage to boiler is less than 90 VAC. “Low 24 VAC” Voltage from transformer is less than 18 VAC. Important Service Reminder: When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. -
Page 47: Error Message "No Flow
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “No Flow” Pump IS NOT Running (If pump is running proceed to the next page) Normally open contacts on factory mounted flow switch are not closing or are not remaining closed after the pump is energized. Pump Relay Note: The style/manufacturer of the pump relay used may change over time. - Page 48 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “No Flow” Pump is Running (If pump is not running go to the preceding page) Normally open contacts on factory mounted flow switch are not closing or are not remaining closed after the pump is energized. Water flow rate at the outlet of boiler is below the activation point for the flow switch.
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Page 49: Error Message "Sequence Err
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Sequence Err” Enable/disable circuit wires to VFD disconnected. 1-10 VDC instruction wires to VFD disconnected. 1-10 VDC instruction wires to VFD reversed polarity. MCB failing to send 1-10 VDC instruction to VFD. “Ignition Speed” Wiring between MCB J24 socket and the Hall Effect Sensor in the blower motor end cap is open or cross connected. -
Page 50: Error Message "Blower Prov Stg1
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower IS NOT Starting (If the blower is starting proceed to the “Blower Prov Stg1” Blower Is Starting tables) IMPORTANT SERVICE NOTE: BEFORE performing any of the check/repair procedures in the right column of this table; review the VFD and Blower Operation section in this manual on page 11. - Page 51 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower IS NOT Starting (If the blower is starting proceed to the “Blower Prov Stg1” Blower Is Starting tables) IMPORTANT SERVICE NOTE: BEFORE performing any of the check/repair procedures in the right column of this table; review the VFD and Blower Operation section in this manual on page 11.
- Page 52 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower IS NOT Starting (If the blower is starting proceed to the “Blower Prov Stg1” Blower Is Starting tables) IMPORTANT SERVICE NOTE: BEFORE performing any of the check/repair procedures in the right column of this table; review the VFD and Blower Operation section in this manual on page 11.
- Page 53 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower Is Starting (If the blower is not starting go to the “Blower Prov Stg1” Blower Is Not Starting tables) Three conditions can cause this error message when the blower is starting: Normally Open Low Blower Prover or High Blower Prover pressure switch contacts are not closing during the pre or post purge operating states - or...
- Page 54 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower Is Starting (If the blower is not starting go to the “Blower Prov Stg1” Blower Is Not Starting tables) Helpful Troubleshooting Note: The state of the contacts for the Low BPS can be viewed in real time using the System Status Menu.
- Page 55 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower Is Starting (If the blower is not starting go to the “Blower Prov Stg1” Blower Is Not Starting tables) Helpful Troubleshooting Note: The state of the contacts for the High BPS can be viewed in real time using the System Status Menu.
- Page 56 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blower Prov Stg1” Blower Is Starting (If the blower is not starting go to the “Blower Prov Stg1” Blower Is Not Starting tables) Three conditions can cause this error message when the blower is starting: Normally Open Low Blower Prover or High Blower Prover pressure switch contacts are not closing during the pre or post purge operating states - or...
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Page 57: Error Message "Blocked Flue
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Blocked Flue” MCB senses the normally closed Blocked Flue (Exhaust) pressure switch contacts are open. Important Service Reminder: When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. Perform a close visual inspection of all wiring and connectors to a given component before replacement. -
Page 58: Error Message "Flame Stg1
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Flame Stg1” Flame or ignition failure. Error message displayed after 1 or 3 losses of flame or after 1 or 3 failed trials for ignition. EMC 5000 control system will lock-out after 1 or 3 trials depending on the SW1 #2 dip switch setting on the MCB circuit board. - Page 59 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Flame Stg1” (cont) Flame or ignition failure. Error message displayed after 1 or 3 losses of flame or after 1 or 3 failed trials for ignition. EMC 5000 control system will lock-out after 1 or 3 trials depending on the SW1 #2 dip switch setting on the MCB circuit board.
- Page 60 ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Flame Stg1” (cont) Flame or ignition failure. Error message displayed after 1 or 3 losses of flame or after 1 or 3 failed trials for ignition. EMC 5000 control system will lock-out after 1 or 3 trials depending on the SW1 #2 dip switch setting on the MCB circuit board.
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Page 61: Error Message "Igniter Stg1
ERROR MESSAGES (CONT) DISPLAYED MESSAGE CONDITION/INDICATES “Igniter Stg1” MCB is not sensing minimum igniter current of 2.7 AC amps during the igniter warm up period. Important Service Reminder: When performing any troubleshooting steps outlined in this service manual always consider the wiring and connectors between components. -
Page 62: Boiler Controls Information
BOILER CONTROLS Boiler controls that are improperly installed or set up can cause serious operational and service related problems such as short cycling. This section provides information for how various controls can work together or independently to provide proper system and boiler control. Two conditions must be met for the VF boiler to start a heating cycle: 1. - Page 63 BOILER CONTROLS (CONT) Primary System Control A Primary System Control is a top level “system” temperature control. A Primary System Control activates the call for heat or enables boiler operation when system temperature falls below the control’s set point and deactivates a call for heat or disables the boiler when system temperature reaches set point.
- Page 64 BOILER CONTROLS (CONT) Controlling Probe The Operating Set Point on the VF boiler’s EMC 5000 control system reacts to temperature sensed by the Controlling Probe. The EMC 5000 control system can be configured to use either the Inlet probe or the remote Tank/Loop probe as the “Controlling Probe.”...
- Page 65 BOILER CONTROLS (CONT) INTERNAL TEMPERATURE CONTROLS (CONT) Automatic High Limit - User Setting “Hi Limit” The Automatic High Limit is a “local” EMC 5000 User Setting that can be adjusted through the UIM (page 8). The Automatic High Limit is a temperature limiting control, it reacts to temperatures sensed at the Outlet Probe (page 62).
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Page 66: External Controls
BOILER CONTROLS (CONT) EXTERNAL CONTROLS Enable/Disable Control Circuit The Enable/Disable Control Circuit is always active. This control circuit must be “closed” to enable boiler operation. Two wires located in the junction box on the back of the boiler are provided for this circuit. From the factory these two wires are wire nutted together. If some form of external control is desired/required, that external control’s “dry”... - Page 67 BOILER CONTROLS (CONT) EXTERNAL CONTROLS (CONT) Types of External Controls An External Control can be a Primary System Control or a Supervisory Control or both. The enable/disable circuit described on page 65 would be field wired to the external control’s dry contacts.
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Page 68: Operating Temperatures
OPERATING TEMPERATURES Temperature rise through the boiler: 20 - 40°F. The temperature rise ( 40°F while firing at 100%. This flow rate maintains a balance between the harmful effects of calcium/lime accumulation (low flow rate) and velocity erosion (excessive flow rate). The will be lower when the firing rate is less than 100%. -
Page 69: Technical Specifications
TECHNICAL SPECIFICATIONS Input Power and Circuit Protection: † Power Supply Voltage 120 VAC Power Supply Requirements Line Protection (MCB) Line Output (Pump) 24VAC Power supply 24VAC Protection †. See page 40 for PDB power supply test procedure. Input Specifications: † Temperature Sensors (Probes) Flame Sensors (2) High and Low fire... - Page 70 TECHNICAL SPECIFICATIONS Input Specifications (cont): † High Blower Prover Pressure Switch † Low Blower Prover Pressure Switch † Blocked Flue (Exhaust) Pressure Switch † Low Gas Pressure Switch † Water Flow Switch † Low Water Cut Off Switch †. Signal level passed through switches: 24 VAC @ >7ma. (Does not require low-level con- tacts).
- Page 71 TECHNICAL SPECIFICATIONS Ignition Timing: Pre-Purge - cold start Pre-Purge – not cold start Shutter Adjust Pre-Circulate Igniter proving time Inter-Purge Post-Purge Pump post-circulate time Default User Settings/Ranges: As shipped from the factory the SW1 dip switches (page 30) on the MCB are preset to the appropriate values according to the system that was ordered, either VW or VB.
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Page 72: Glossary
GLOSSARY T: Symbol used for “Delta T.” Engineering term to convey “temperature rise” or “difference” Δ through a boiler or heat exchanger. IE: If the inlet water temperature to a boiler is 120°F and the outlet water temperature leaving the boiler is 140°F; the temperature rise through the boiler is 20°F, which is commonly expressed as “20°... - Page 73 GLOSSARY (CONT) UIM - User Interface Module: Plastic housing that holds the UIB, LCD, and TSB. Provides means to both send and receive information from the user. Only one cable to the MCB is required for communications and power. Operates on 5 VDC only. Connects to internal communications port on MCB, see page 32.
- Page 74 Service Handbooks. For additional information contact: A. O. Smith Water Products Company A Division of A. O. Smith Corporation 500 Tennessee Waltz Parkway Ashland City, TN 37015 1-800-527-1953 www.hotwater.com Part No. TC-099 ©2007 A. O. Smith Corporation...