A.O. Smith TC-099, Service Handbook

Page 1: ...ariable Fire Boiler Domestic Hot Water Hydronic Heating VF Boiler 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 Service Handbook Part No TC 099 Printed in the U S A 0407 ...

Page 2: ...eck Control Panel Layout MCB Modulation Control Board PDB Power Distribution Board 2 2 2 3 4 4 6 7 8 9 11 11 12 13 14 15 17 19 20 23 24 25 35 Troubleshooting Error Messages Display Is Blank Error Message Display Fail Error Message No Config Key Error Message Config Key CRC Error Message Config Key Part Error Message Low AC Voltage Error Message Low 24 VAC Error Message Low Water Error Message Low ...

Page 3: ...ervice manual is not a complete installation instruction Installation information covered in this service manual has a limited focus as it applies to servicing the boiler This Service Manual does not replace or supersede the Instruction Manual that came with the boiler Always refer to the Instruction Manual that came with the boiler for complete installation instructions Qualifications Service of ...

Page 4: ...However their resolution is insufficient to be used for measuring draft manifold gas pressure on VF boilers or perform air pressure switch testing U tube manometers or gas pressure gauges may not be substituted for Digital Manometers listed below Digital Manometer s range 20 00 to 20 00 W C resolution 0 01 W C Recommend UEI model EM200 or equivalent Used to test performance of air pressure switche...

Page 5: ...mental conditions that may be contributing to a problem with operation or a lock out Short cycling protection if any stage logs more than 30 cycles in one hour the control enters a short cycle prevention condition The boiler will continue to operate in this mode The UIM will display and log a Short Cycle Cond error message with the yellow Standby system status LED flashing The MCB will add a 180 s...

Page 6: ...he right of the LCD Firing Rate Status indicator located in the lower right portion of the UIM Four LED lights behind a green gradient translucent cover This display indicates the approximate firing rate between 25 and 100 LCD Liquid Crystal Display LCD display 4 lines up to 20 characters per line 10 different screens Menus Temperatures System Status Control States User Settings Configuration Sett...

Page 7: ...fter 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 Hard lock outs can only be reset by touching the Select button while the error screen is displayed Power interruptions or cycling the power on and off will not reset hard or soft lock outs The ...

Page 8: ...ed to Touch once to display helpful information about the current menu screen Touch a second time to return to previous screen Touched from the main menu screen and the UIM displays general information on how to use the EMC 5000 user interface Up and Down Buttons are used to Scroll or navigate up and down lists of menu screens and menu items When the current menu contains more than four lines of t...

Page 9: ...the lower right corner this indicates there are more menu items below the four lines currently being displayed Up arrows appear on the top right corner when there are more menu items above Screen Display 5 the Select button is touched once to enter the User Settings menu Screen Display 6 shows the first four lines of the User Settings menu Touching the Select button while the sign is lined up with...

Page 10: ...r inputs available from this screen System Status Screen This screen is used to view the status of switch inputs and output states An asterisk is displayed next to the label when the status is True the description is fulfilled For example if water is flowing as detected by the flow switch an asterisk will appear in front of the Flow label IE Flow There are no adjustable user inputs available from ...

Page 11: ... still valid When cleared it is moved to the Error History Screen The system will automatically jump to this screen when an error is detected It will also go to this screen upon power up if an error was still valid when power was turned off Errors are cleared control system is reset from this screen by touching the Select button There are no adjustable user inputs available from this screen Error ...

Page 12: ...d precisely by modulating the frequency Hz of the power supplied to the blower motor VFD output to the blower is a 3 Phase power supply Three conditions must be met before the VFD will start the blower 1 120 VAC is supplied to the VFD 120 VAC input 2 The MCB closes an enable disable circuit that enables VFD operation 3 The MCB sends a 1 10 VDC instruction to modulate blower speed The DC voltage in...

Page 13: ...ocity of air flowing through the Venturi is also increased This further increases the vacuum created by the Venturi and more fuel gas is pulled from the gas valve This increases the firing rate input Btu hr of the VF boiler As the blower speed is decreased less fuel gas is supplied and the firing rate is reduced The MCB controls blower speed according to temperature demand When system temperature ...

Page 14: ... speed See the images below Example If the MCB has sent an 4 3 VDC instruction to the VFD to run the blower at 2500 rpm and the actual rpm relayed back from the Hall Effect sensor indicates the blower is running at 2400 rpm the MCB will adjust increase the DC volt instruction slightly until the actual rpm information matches the instruction sent by the MCB See VFD and Blower Speed operation on pag...

Page 15: ...rom the Config Key into it s own internal memory The MCB then uses the data to modulate blower speed by sending 1 10 VDC instructions to the VFD page 11 Modulating blower speed also modulates the firing rate on VF boilers page 12 There is a label at the end of the Config Key cable near the memory chip This end of the cable is threaded into the wiring chase during production The quickest way to ver...

Page 16: ...eat is activated Call For Heat is Activated High Blower Prover Switch Contacts Verified Open Boiler enters Service Mode and locks out UIM displays Blower Prov Stg1 Error message NO Blower Is Energized By VFD Pre Purge State approx 5000 rpm 10 30 Seconds Low Blower Prover Switch Contacts Verified Closed High Blower Prover Switch Contacts Verified Closed Boiler enters Service Mode and locks out UIM ...

Page 17: ...taneously Only key events are shown in order to provide a general understanding of how the control operates Event timings can vary depending on actual conditions SERVICE NOTE VF boilers utilize two flame sensors One is positioned closer to the buner than the second to enable flame detection during low and high fire conditions The wiring from the two flame sensors is joined and connects to a single...

Page 18: ...up with the User Settings menu and press the Select button Scroll down to Mod Mode menu item and press the Select button again The cursor starts flashing on and off slowly indicating adjustment of this menu item is now possible Use the up and down buttons to select between these three options Min forced minimum firing rate 25 Max forced maximum firing rate 100 Mod MCB automatic controlled firing r...

Page 19: ...declare a fault This will verify that the pump flow switch igniter VFD variable frequency drive gas valve blower and low high blower prover switches are all functioning 8 Drill a 7 16 hole in the side of the boot tee approximately 8 from back panel to insert the gas analyzer probe The hole must be sealed upon completion of the start up 9 Open the main supply gas valve to the boiler 10 Turn the boi...

Page 20: ... gas valve Using a TORX T40 or a 5mm hex wrench carefully turn the low fire adjustment screw under the cap clockwise to increase or counterclockwise to decrease gas flow and achieve the desired CO2 level per low fire table below When desired adjustments are complete reinstall the cap on the gas valve CO readings should be less than 200 ppm Start Up Note There will be a time delay between adjustmen...

Page 21: ...uivalent to 10 linear feet of pipe on VF boilers If the boiler is in an equipment room with a door to the outdoors temporarily disconnect the intake air pipe and prop open the equipment room door Take combustion readings again to see if this corrects the problem Conventional Vent Installations If the boiler is using room air for combustion ensure the vent pipe has not exceeded the 100 maximum equi...

Page 22: ... Mode Firing Modes page 17 Start the boiler and check the three parameters listed below during the three operating states given above DC voltage sent by the MCB at the VFD page 11 Actual blower rpm as sensed by the Hall Effect sensor page 13 Actual power frequency Hz on the VFD display page 11 Procedure Measure the DC volt instruction from the MCB at the VFD to ensure all wiring and connections be...

Page 23: ...Purge Mode Approx RPM 5000 5000 5000 Blower Speed Ignitor Warm Up Period Approx RPM 2200 2200 2200 Blower Speed Min Mode 25 Approx RPM 800 1200 1250 Blower Speed Max Mode 100 Approx RPM 2500 4100 4500 Blower Power Freq Pre Post Purge Mode Approx Hz 172 Hz 172 Hz 179 Hz Blower Power Frequency Ignitor Warm Up Period Approx Hz 75 Hz 75 Hz 75 Hz Blower Power Frequency Min Mode 25 Approx Hz 26 Hz 41 Hz...

Page 24: ...e below Service Note If the actual pressures observed during the test above are considerably different higher pressures closer to a positive pressure closely inspect all fittings and flanges in the gas train between the outlet of the boiler s 24 VAC gas valve and the Venturi assembly See page 12 Reseal repair any leaking connections replace any worn or damaged gaskets Disassemble the Venturi from ...

Page 25: ... is running See the Sequence of Operation on page 15 Note which sensing ports are used The two sensing ports on each pressure switch are differentiated with the letters L and H embossed on the switch body The sensing tubes must be connected to the ports marked L The other port remains open The barbed fitting for the H port is typically cut off at the factory to ensure proper connection The two sen...

Page 26: ...the UIM pages 4 and 14 menu screens on VF boilers it is referred to as the CCB Some UIM menu screens show the term FCB flame control board The FCB is a portion of the MCB that controls ignition It is not a separate part The EMC 5000 control system is used on other products such as Genesis boilers that are staged boilers and do not have modulating burners However this MCB circuit board is not an in...

Page 27: ...ing and connection information shown in this service manual are in reference to how the EMC 5000 controls and circuit boards connect on VF boilers This service manual should be used as a reference for A O Smith VF boilers only The MCB circuit board measures approximately 13 x 7 and has 16 Molex AMP socket connectors The MCB circuit board has been divided into sections in the illustration below eac...

Page 28: ...s 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 Pin 1 24 VAC line Pin 2 24 VAC line Pin 3 Ground A Red LED Illuminated when F1 fuse is blown F1 Fuse 24 VAC 7 5 amp J3 Socket 24 VAC power supply from transformer 3 2 1 The MCB circuit board is mounted upside down on VF boilers compa...

Page 29: ...ched 24 VAC control circuits with a maximum amp rating of 1 amp When these optional components are used the MCB must be configured to recognize and enable the components by setting the SW1 dip switches accordingly See page 30 B 2 1 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 3 2 1 6 7 8 9 10 1 2 3 4 5 6 J4 Outputs J11 Tstat J5 Inputs J17 BlwPrv Hi Gas J19 Gas Valve The MCB circuit board is mounted upside down ...

Page 30: ...120 VAC hot wire Pin 2 120 VAC neutral wire Pin 3 Ground J18 Socket Silicon Carbide igniter power Pin 1 Igniter 120 VAC hot wire Pin 2 Igniter 120 VAC neutral wire F2 Fuse N A on VF boilers if fuse is removed or blown it will not effect operation of VF boiler JP4 Jumper Should be on removed during manufacturing only J16 Flame Flame sensor connection single wire connect on MCB split wire serves two...

Page 31: ...itch 4 Controlling probe On Tank Loop Remote Off Inlet Switch 5 Power vent kit N A set to off On Yes Off No Switch 6 Low water cut off present On Yes Off No Switch 7 Low gas pressure switch present On Yes Off No Switch 8 The control system will not initiate blower operation on VF boilers if dip switch 8 IS NOT set to on for modulating burner operation The pump will start but the blower will not Af...

Page 32: ...ires from this socket are routed to the junction box on the back of the boiler Dedicated field wiring and conduit must be routed between the Tank Loop probe and the junction box The remote Tank Loop temperature probe is factory supplied with VF boilers This temperature probe is used as the Controlling Probe pages 62 and 63 on VF boilers SW1 dip switch 4 must be turned on to activate the this probe...

Page 33: ...ked daisy chained together in this way For a boiler to be seen on the network it s default network address of 0 must be changed to a number between 1 and 31 in the User Settings menu from the UIM Each boiler on the network would need to have a different network address Internal Comm Ports 2 These are parallel ports used to connect internal components that communicate with the MCB One is reserved f...

Page 34: ...must be configured correctly dip switch 3 does not affect operation on VF boilers Switch 1 Spare On Off Switch 2 High gas pressure switch is optional this switch must be set to Off if there is not a high gas pressure switch installed on the boiler High gas pressure switch present On Yes Off No Switch 3 The position of this dip switch on VF boilers has no effect on operation Number of blower speeds...

Page 35: ...the MCB will read 0 rpm even though the blower is running The control system would then lock out and display the Ignition Speed error message The MCB contains a resistor for the VFD enable disable circuit to limit current There is approximately 1100 ohms resistance when this circuit has been closed by the MCB use a 2000 to 20 000 ohm scale on the ohm meter being used The audible continuity test fe...

Page 36: ...ower supply protection Wiring and connection details given here reference 100 101 Series VF boilers The wiring and connection information given in this document is in reference to how the EMC 5000 controls and circuit boards connect on 100 101 Series VF boilers This control system may be used on other products such as Genesis boilers and while some wiring and connection information will be the sam...

Page 37: ...per NEMA standards using a 30 amp dedicated circuit breaker The power supply must be in a dedicated conduit Hot wires neutral wires and ground wires must not be shared with any other appliances including other VF boilers External control or Tank Loop Probe wiring must also be in dedicated conduits See the power requirements on page 68 1 2 3 4 5 6 7 8 9 10 A Ground To Boiler JP2 Jumper Should be on...

Page 38: ...se on board remote pump relay connected to TB1 terminal board on the PDB page 36 For 120 VAC outputs between 5 and 20 FLA use an external relay starter and supply 120 VAC pump power through the 20 amp F2 pump fuse on the PDB shown above For outputs above 120 VAC or 20 FLA use an external relay starter and a separate dedicated power supply for the pump use the on board pump relay Com and N O contac...

Page 39: ...rs Pin 5 24 VAC Return to Stage 2 FCB N A on VF boilers Pin 6 N A Pin 7 N A Pin 8 24 VAC Hot to Stage 3 FCB N A on VF boilers Pin 9 24 VAC Return to Stage 3 FCB N A on VF boilers Pin 10 24 VAC Hot to Stage 4 FCB N A on VF boilers Pin 11 24 VAC Return to Stage 4 FCB N A on VF boilers Pin 12 N A J1 Socket 100VA Transformer 120 VAC x 24 VAC Pin 1 24 VAC Common Pin 2 24 VAC Hot Pin 3 120 VAC Hot to Tr...

Page 40: ... 3 Earth Ground to MCB J1 Socket Pin 4 120 VAC Hot to VFD Input Terminals page 11 Pin 5 120 VAC Neutral to VFD Input Terminals page 11 Pin 6 Earth Ground to VFD Input Terminals page 11 Pin 7 Spare 120 VAC Hot Pin 8 Spare 120 VAC Neutral Pin 9 Spare Earth Ground Pin 10 Spare 120 VAC Hot Pin 11 Spare 120 VAC Neutral Pin 12 Spare Earth Ground Pin 13 Spare 120 VAC Hot Pin 14 Spare 120 VAC Neutral Pin ...

Page 41: ...en LEDs should be illuminated and the red LED should be off If any other combination of LEDs are illuminated refer to the table below for the problem indicated and what corrective action must be taken Note The JP1 jumper should be in the run position during normal operation Leaving the jumper in the test mode when operating the system may cause trouble with Ground Fault Interrupters The wire harne...

Page 42: ...by the flow switch flow switch contacts are closed an asterisk will appear in front of the Flow menu item Flow Things to check before servicing Using the Instruction Manual that came with the boiler as reference verify the water piping gas line venting electrical and controls are all properly installed Ensure SW1 dip switch 8 is turned on for Single Modulating Burner operation page 30 Ensure the C...

Page 43: ...and install a new comm cable standard Cat 5 net work cable Plug UIM comm cable into other internal comm port on the MCB page 32 Closely inspect communication ports on MCB and UIM for damage or wear page 32 Ensure 120 VAC power is properly connected in the junction box on the back of the boiler Ensure 120 VAC is supplied to TB1 terminals 8 and 9 on the PDB Hot wire to terminal 8 neu tral wire to te...

Page 44: ...ion Plug UIM comm cable into the other internal comm port on the MCB see page 32 Check comm cable to the UIM Turn off power and Install a new different comm cable standard Cat 5 network cable Inspect both internal communication ports on MCB and UIM for damage or wear Repair or replace any components that are worn or dam aged No Config Key MCB does not recognize the presence of a Config Key at MCB ...

Page 45: ...ng to perform this step thoroughly often results in needless down time unnecessary parts replacement and customer dissatisfaction Ensure the Config Key is securely plugged into the J23 socket on the MCB circuit board see pages 14 and 34 Turn power off to the boiler for 1 minute and then turn power back on Press the Select but ton on the UIM to clear any error messages This will provide the MCB a s...

Page 46: ...ansformer if rating is less than 100 VA Secure power to boiler temporarily disconnect load wiring from secondary coil on transformer Turn power back on and check voltage at sec ondary coil if secondary 24 VAC voltage remains low replace transformer Check all 24 VAC wiring for worn damaged con nections or wires replace repair as necessary Replace transformer Low Water Water is not being sensed by o...

Page 47: ...rm this step thoroughly often results in needless down time unnecessary parts replacement and customer dissatisfaction VB Models No Factory Pump Check for power at the pump motor if the pump has power but will not start replace repair pump If power to the field installed pump is not present ensure all field installed pump controls wiring connectors and relays or starters are function ing correctly...

Page 48: ...fore performing the check repair procedures here New boiler installations in older systems Check for restrictions in the water lines accu mulated lime to and from the boiler System lines can become restricted with lime and sedi ment accumulation over time and sometimes must be replaced on older systems New boiler installations in older systems Ensure existing water lines to and from the boiler are...

Page 49: ...ase See pages 13 and 34 Close visual inspection of J24 plug socket con nection on MCB Daughter Board Ensure plug socket connect is in good condition and making good contact See page 34 Remove end cap from blower motor and inspect Hall Effect sensor for any sign of damage or wear Ensure Hall Effect sensor is properly mounted Mtr Spd Min Spd One or more wiring connections between MCB J24 socket and ...

Page 50: ...ep or failing to perform this step thoroughly often results in needless down time unnecessary parts replacement and customer dissatisfaction SW1 dip switch 8 is in the off position this dip switch must be in the on position page 30 Turn off power to boiler and disconnect the wires to both BPS BPS Blower Prover Switches check for continuity between the Com and N O terminals on both BPS If there is ...

Page 51: ...unnecessary parts replacement and customer dissatisfaction Ensure all wiring is reconnected to the VFD and all plugs are securely plugged into the MCB PDB With power on and a call for heat acti vated check for a 1 10 VDC instruction from the MCB at VFD low voltage terminals 0V and AI1 see VFD connections on page 11 See also the Firing Rate Modulation Performance section on page 21 and VFD Operatin...

Page 52: ...ce 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 Ensure wires were stripped before being crimped in a wire connector ensure wires are crimped tightly in their connectors ensure connection pins in sockets and plugs are not damaged or worn ensure plugs and sockets are mating p...

Page 53: ... switches close on a fall in pressure the pressure sensed must be in a vacuum Operational Note See blower prover switch information on page 24 and the Sequence of Operation on page 15 Ensure the sensing tubes are connected to the L sensing ports on both BPS BPS Blower Prover Switches see the control panel layout and pressure switch information on page 24 Ensure all BPS sensing tubes are not kinked...

Page 54: ...wer failure during the heating cycle or if the pressure sensed by the switch rises above the switches activation pressure for any reason The normally open contacts on both Blower Prover switches close on a fall in pressure the pressure sensed must be in a vacuum Operational Note See blower prover switch information on page 24 and the Sequence of Operation on page 15 Determine if Low BPS is causing...

Page 55: ...fall in pressure the pressure sensed must be in a vacuum Operational Note See blower prover switch information on page 24 and the Sequence of Operation on page 15 Determine if High BPS is causing the lock out The normally open High BPS BPS Blower Prover Switch switch must close its contacts during the Pre and Post purge operating states only This is when the blower is running at approximately 5000...

Page 56: ...uence of Operation on page 15 Pressure Reading Test Take a manifold gas pressure reading See page 23 for how to perform this test Allow the boiler to operate until the Pre purge cycle com pletes and the blower speed reduces for igni tion Record the highest and lowest pressures observed This may require jumpering the BPS switches as described on pages 53 and 54 This pressure must be between 0 12 W ...

Page 57: ... a normally closed switch Check all wiring between the Blocked Flue Switch and the MCB J5 socket pins 5 6 page 28 Closely inspect the J5 socket plug repair replace anything worn or damaged Disconnect the sensing tube from the Blocked Flue Switch Take a pressure reading with a dig ital manometer from this end of the sensing tube with the boiler firing at 100 Turn the boiler on and put the boiler in...

Page 58: ...es on pages 20 23 View the burner through the view port near the igniter on the top of the combustion chamber during the ignition trial period If the burner is igniting but the flame goes out in a few seconds ensure the flame sensor wiring is connected properly and in good condition Note There are two flame sensors on VF boil ers A single wire is connected to the J16 con nect on the MCB page 29 Th...

Page 59: ...ten results in needless down time unnecessary parts replacement and customer dissatisfaction Check igniter amperage during igniter warm up period If amp draw is less than 3 0 amps replace the igniter Ensure the 1 8 steel sensing tube that connects between the gas valve near the low fire adjust ment screw cap and the Venturi assembly is not clogged or damaged and properly con nected at both ends If...

Page 60: ...ure power to the boiler Remove the gas pressure test plug at the outlet of the boiler s 24 VAC gas valve Install a barbed hose adapter fit ting in this test port Connect a U tube or digital manometer to the barbed fitting Close the gas train shut off valve see image on page 23 Turn power to the boiler back on ensure there is a call for heat present The blower will reduce speed as the igniter warm ...

Page 61: ...ing properly and providing good contact Failure to perform this critical step or failing to perform this step thoroughly often results in needless down time unnecessary parts replacement and customer dissatisfaction Check all wiring and connections between pins 1 2 of the J18 socket on the MCB see page 29 and the igniter Repair replace any worn or damaged wiring or connectors Closely inspect the p...

Page 62: ...ndependently or work with an external supervisory control utilizing the Enable Disable circuit 2 The Enable Disable circuit page 65 must be closed Two wires are provided in the wiring junction box on the back of the boiler for this circuit The Enable Disable circuit is provided to allow the VF boiler to be started or stopped by different forms of external supervisory controls page 65 including Aqu...

Page 63: ...rs A change in temperature causes a corresponding change in electrical resistance ohms The EMC 5000 control system interprets the probe resistance as temperature VF boilers have two factory installed temperature probes an Inlet Probe and an Outlet Probe to monitor the inlet and outlet water temperatures VF boilers are shipped from the factory with a third probe the remote Tank Loop Probe Remote Ta...

Page 64: ... to temperature sensed by the Controlling Probe When the temperature sensed at the Controlling Probe drops below the Operating Set Point minus the Stage 1 Differential AND the Enable Disable circuit page 65 is closed a call for heat is activated When an external control is used as the Primary System Control set the Operating Set Point at least 20 F higher than the Primary System Control setting to...

Page 65: ...e programmed for more than 20 F above Operating Set Point but not for less The Operating Set Point cannot be raised higher than 20 F below the Automatic High Limit Hi Limit set point Keep this in mind if the Operating Set Point seems stuck or will not allow higher settings within it s range You may have to raise the Hi Limit set point first Automatic High Limit Differential User Setting Hi Limit D...

Page 66: ...d conduit page 68 The external control can then enable disable the boiler by closing or opening its contacts When the external control opens it s contacts the boiler is disabled and goes through a normal shut down sequence the gas valve s close blower s run for a programmed post purge period and the boiler goes into standby mode If no external control is used connected to this circuit the two wire...

Page 67: ...ed by an EMS control equipped with it s own Tank Loop temperature sensor Supervisory functionality such as occupied unoccupied and or freeze protection can be programmed in EMS systems to enable or disable boiler operation based on temperature time and event programing Outdoor Air Reset Control is another functionality EMS controllers often provide The EMS system will have an outdoor temperature s...

Page 68: ...ter systems DO NOT connect the cold water make up line to the boiler return inlet piping as this will make maintaining 120 F minimum inlet water temperature more difficult Bypass Lines Bypass lines should be installed on all VF boilers to maintain a minimum inlet water temperature of 120 F Bypass lines feed a portion of the outlet water back to the inlet of the boiler which raises the inlet water ...

Page 69: ...dicated conduit Flame Sensors 2 High and Low fire 5µA DC micro amps current typical Flame detection failure occurs under 2 5 µA Igniter Silicon Carbide 40 to 70 ohms cold 3 0 to 4 0 AC amps typical minimum proving current of 2 7 AC amps AC Line Polarity Sensor Detects reversed power connections and unconnected ground leads on power lines referenced to earth ground ECO Switch 24 VDC Normally Closed...

Page 70: ...r level is low High Speed Combustion Blower 120 VAC 50 60 Hz 3A MCB J15 Socket Low Speed Combustion Blower 120 VAC 50 60 Hz 3A MCB J15 Socket Hot surface igniter Silicon Carbide 120 VAC 50 60 Hz must prove 2 7 AC amp minimum Gas Valve 24 VAC 50 60 Hz Switched 3 5 A Low Water Cut Off 24 VAC 50 60 Hz Not Switched 1 A Alarm 24 VAC 50 60 Hz Switched 1 A Spare 24 VAC 50 60 Hz Switched 1 A IRI Gas Valve...

Page 71: ...st circulate time Selectable 45 90 180 seconds or continuous VW MODELS DEFAULT SETTING ADJUSTABLE RANGE Oper Setpnt Operating Setpoint 145 F 63 C 70ºF to 190ºF Stage1 Diff Operating Setpoint Differential 3 F 2 C 1 to 50 F Hi Limit Automatic High Limit Setpoint 210 F 99 C 90ºF to 210ºF Hi Limit Dif Automatic High Limit Differential 20 F 11 C 1 to 50 F VB MODELS DEFAULT SETTING ADJUSTABLE RANGE Oper...

Page 72: ... a fall in pressure It is used to detect that the blower is running during the heating cycle Connects to J17 socket on MCB see pages 24 and 28 Low Gas Pressure Switch This is a normally open pressure switch that closes on a rise in pressure used to detect supply gas pressure is maintained above minimum requirement This switch is standard on VF boilers Connects to J5 socket on MCB see page 28 The M...

Page 73: ...DC only Connects to internal communications port on MCB see page 32 VFD Variable Frequency Drive A component that varies the power supply s frequency Water Flow Switch This is a normally open paddle type switch mounted in the outlet of the boiler that closes when water flow through the boiler exceeds the minimum flow make point of the switch This switch does not prove required flow rate only that ...

Page 74: ...mation Central link of www hotwater com for a listing of available 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 ...