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35

Mascot LX Service Manual

Troubleshooting the 24V DC Power Supply

B2

Many of the controls in the boiler operate on 24V, including:

•  The SIT controller and display panel
•  Most of the sensors and switches that provide inputs for the controller.
Figure B1-1 in the last section shows the power distribution system.  A transformer

develops 24V AC, which is later rectified to produce 24V DC.
There are two safety devices we should point out:
• A 2A circuit breaker for the 24V DC supply. This is mounted behind the lower

front cover. See Fig. B2-1

• F3, an 800 mA fuse, located on the back of the control board. The instructions

in Section B1 explain how to reach this fuse.

Some of the parts inside the power box can carry full line voltage. This voltage can

cause death or serious personal injury. Do not open this box or work inside unless

you have been trained in safe electrical service techniques.

Fig. B2-1 - Circuit breaker for 24V DC

(Shown with lower front cover removed)

2A circuit breaker for

24V DC power supply

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Содержание MASCOT LX

Страница 1: ...vice Manual for Mascot LX Modulating Boilers Model MLXH Sizes 50 75 100 150 175 and 220 MBTU h Water Heaters Model MLXC Sizes 125 150 and 175 MBTU h Modulating Boilers Model MLXH Sizes 50 75 100 150 1...

Страница 2: ......

Страница 3: ...ations 8 Access to Control Board 9 Control Panel 10 Control Display 11 Operating Displays 12 Operating Displays Examples 13 Notifications Blocking Lockout and Error Displays 14 Changing Setpoints 16 I...

Страница 4: ...lower Problems 43 B12 Air Pressure Switch 45 B13 Gas Valve 47 B14 Condensate Trap 48 B15 Pressure Relief Valve 49 B16 Direct Spark Ignition 50 B17 Pump Problems 52 B18 Outdoor Reset 53 B19 Low Water C...

Страница 5: ...bleshooting Combustion Problems 74 C4 Cleaning the Burner and Heat Exchanger 75 Appendix Sect Title Page App1 SIT Parameter Codes 77 Lockout Codes 77 Blocking Codes 77 Notification Codes 78 Installer...

Страница 6: ...Mascot LX Service Manual iv...

Страница 7: ...ormation from the listing in Section App1 in the Appendix This manual covers two versions of the Mascot LX The standard unit MLXH which produces hot water for central heat only This type of unit can a...

Страница 8: ...ader includes several ways of locating information From the line at the top of the screen select Edit then Find Type in the item you want to find The PDF Reader will take you to the first occurrence o...

Страница 9: ...m age Improper installation and or operation will void the warranty Fire or Explosion Hazard Improper configuration can cause fuel buildup and explosion Improper user operation may result in death sev...

Страница 10: ...nce of local codes with 1 The National Electrical Code ANSI NFPA No 70 latest Edition or 2 CSA STD C22 1 Canadian Electrical Code Part 1 This appliance must be electrically grounded in accordance with...

Страница 11: ...Installation Codes All installations must be made in accordance with 1 American National Standard Z223 1 NFPA54 Latest Edition National Fuel Gas Code or 2 CSA B149 1 Natural Gas and Propane Installat...

Страница 12: ...g the Covers The upper and lower covers can be removed by pulling the part straight out and away from the unit The center control panel cannot be re moved Upper inner panel 2 screws Lower inner panel...

Страница 13: ...utlet pipe top Water outlet pipe bottom Air bleed vent Pressure switch Blower Heat exchanger Transformer Condensate trap Circulator pump Three way valve Combi units only Burner inside heat exchanger V...

Страница 14: ...witch Inlet water temp sensor Water pressure switch Air vent Water outlet temp sensor and safety limit Low water cutoff switch optional Flue temp sensor and flue safety DHW water temp sensor DHW flow...

Страница 15: ...Mascot LX Service Manual 9 Access to Control Board Lower metal panel folds down High voltage terminal strip The controller circuit board is located behind this cover...

Страница 16: ...n display screens or to change values used by the unit Reset button Use this to reset the controller after a lockout OK Select button Use this to select one of the options or to Save a changed value C...

Страница 17: ...w display ing system temperature Now display ing domestic hot water temperature Now displaying stack temperature Now display ing inlet tem perature Now display ing outlet temperature Flame size indica...

Страница 18: ...F 189 F default 130 F Burner rate if the burner is lit You can also use the Up and Down buttons to step through these displays The following images show how to interpret these displays Operating Mode...

Страница 19: ...F at outlet sensor System temp display temp is 188 F Outlet sensor Central heat demand System temp sensor or Operating Displays Examples Outlet sensor temp 180 F Inlet sensor temp 150 F Delta T 30 F...

Страница 20: ...tion A3 Blocking A Blocking code also indicates an unusual condition that will not prevent the unit from operating During a blocking event the unit is correcting itself or moving toward normal operati...

Страница 21: ...LX Service Manual 15 Notification Blocking Lockout and Error Displays continued Error An Error display indicates a problem with the SIT control board For instructions on replacing the board see Secti...

Страница 22: ...you see the display for the setpoint you want to change or Press the Up and Down buttons to go to the display which includes the setpoint you want to change In this example this will be the Central H...

Страница 23: ...or five seconds You should see U00 to indicate you have entered Installer mode 2 Press OK Select again The display will blink 3 Use the Up button to change the value to 15 then press OK Select again 4...

Страница 24: ...Mascot LX Service Manual 18...

Страница 25: ...l settings Yes No Is the red Power light on Check for a problem with the incoming line voltage Is the unit plugged in Check the 120V power supply See Section B1 Yes No Is the display panel lighted Che...

Страница 26: ...ert a jumper to create a permanent Call For Heat terminals 5 and 6 on the low voltage terminal strip Yes No Does the Central Heat or System symbol light up Replace the SIT controller board See Section...

Страница 27: ...g you should see zero volts and zero across these contacts No Is the air pressure switch closed See Section B12 Air Pressure Switch Yes No Programming is correct See Operating Displays and Changing Se...

Страница 28: ...ancel the lockout Power down the unit wait two minutes then power on the unit again If this does not restore normal operation replace the SIT control board See Section B30 E002 Fan speed error There h...

Страница 29: ...e control board See Section B30 E005 Water pressure switch error There has been a lockout because of the problem with the water pressure switch Check the water supply to the unit The switch will not c...

Страница 30: ...ocked vent fan proving switch error There has been a lockout because the controller did not detect a normal airflow through the system Check for a blockage in the vent Check the wiring to the air pres...

Страница 31: ...s does not restore normal operation replace the SIT control board See Section B30 E014 Outlet high temperature manual reset high limit Check for a blocked flue Check the wiring to the outlet water tem...

Страница 32: ...ry E017 Flue sensor error Check the wiring to the sensor See Section B8 Replace the sensor if necessary E018 Outlet sensor error Check the wiring to the water outlet temperature sensor See Section B4...

Страница 33: ...boiler will continue to run at Low Fire If this condition continues the controller will present a Lockout message Once the problem has been corrected press Reset to remove the limitation N03 Fan spee...

Страница 34: ...ure sensor and replace it if necessary See Section B6 N06 Outdoor temperature sensor not present This may mean that the sensor is disconnected or not working If this condition continues the controller...

Страница 35: ...blower Yes No Yes No Clear it Air inlet is blocked No Yes See the sections on Operating Displays and Changing Setpoints CH or System setpiont is correct Pump s working correctly Yes See Pump Problems...

Страница 36: ...r to install a buffer tank A similar situation can occur if the boiler is connected to an indirect DHW tank If the output of the boiler is too large in relation to the size of the tank the system may...

Страница 37: ...LX Service Manual On systems using anti freeze This can occur if the concentration of anti freeze is too high At concen trations above 35 localized boiling can occur and this can produce noise A6 Unit...

Страница 38: ...32 Mascot LX Service Manual...

Страница 39: ...pump Three way valve Figure B1 1 is a circuit diagram Some of the parts inside the power box can carry full line voltage This voltage can cause death or serious personal injury Do not open this box or...

Страница 40: ...ng the fuses on the control board 1 Turn off the power switch on the front panel 2 Remove the lower front panel 3 Remove the two screws shown in Fig B1 3 4 The front panel is hinged Swing it down 5 Yo...

Страница 41: ...fety devices we should point out A 2A circuit breaker for the 24V DC supply This is mounted behind the lower front cover See Fig B2 1 F3 an 800 mA fuse located on the back of the control board The ins...

Страница 42: ...panel 2 Remove the lower front cover The inlet water tem perature sensor is mounted in the lower left corner of the unit See Fig B3 1 3 Unplug the wiring connector two wires The con nector is locked i...

Страница 43: ...Procedure Tools and equipment required 17 mm wrench or crescent wrench Pipe dope or Teflon tape Procedure 1 Turn off power to the unit Use the main discon nect switch mounted on the front panel 2 Iso...

Страница 44: ...m with the DHW sensor it will present a n05 fault message For more information see Section B25 or B27 To check the sensor for accuracy see Section B9 System Sensor DHW Sensor The Outdoor sensor is mou...

Страница 45: ...exchanger Actual stack temperature problem Check the wiring at the sensor and connector X4 on the control board Insert a probe inside the terminal Wiring to sensor is correct Good connections No Yes...

Страница 46: ...Turn off power to the unit Use the main disconnect switch on the front panel 2 Turn off all gas valves supplying gas to the unit 3 The stack temperature limit switch is mounted in the exhaust duct on...

Страница 47: ...sor assembly actually uses two thermistors The control module compares the readings of the two If the difference the drift becomes greater than allowed the controller declares a lockout and prevents t...

Страница 48: ...d upstream and downstream of the unit 4 Drain the boiler 5 The water pressure switch is mounted in the upper left corner of the cabinet as shown in Fig B10 1 To get access to the switch remove the upp...

Страница 49: ...air intake and exhaust vents Test the air pressure switch Want continuity when blower is on Switch should be open when blower is off Remove the blower and check it See the instructions in this sectio...

Страница 50: ...left 7 In order to remove the blower you will need to get the spark rod and flame sensor out of the way Re move these parts as shown in Fig B11 2 8 Loosen the union nut between the gas inlet pipe and...

Страница 51: ...ir intake and exhaust vents Remove the blower and check it See the instructions in this section Mechanical problem with blower Yes No Test the air pressure switch Switch is OK No Replace the bad switc...

Страница 52: ...proving switch The switch measures the difference in air pressure between the Venturi and the flue collector Because the switch is normally open N O you should see continuity across the switch contac...

Страница 53: ...ll Phillips head screw 5 Undo the two cap head screws that support the end of the air line This assembly hangs from the end of the Venturi The air line runs to the air pressure switch Once the assembl...

Страница 54: ...it is easy to clean Remove the cap and flush out this area at least once a year On a Mascot LX unit the condensate trap is installed outside of the cabinet so it should be easy to reach Note that the...

Страница 55: ...alve from the water outlet pipe using the two pipe wrenches 5 The replacement valve must be the correct size and capacity to match the size of the Mascot LX unit Check the old valve for two important...

Страница 56: ...he ignition system during normal operation Electrical Shock Hazard While the burner is lighting the controller will generate a high voltage between the spark rod and the ground rod Use care when worki...

Страница 57: ...he spark rod and the ground rod See Fig B16 3 The clearance should be 3 16 5 mm 9 If the assembly is damaged replace it by reversing the instructions listed above Remember to remove the jumper you ins...

Страница 58: ...ge terminals Boiler pump 4 5 System pump 6 7 DHW pump 8 9 Pump is getting power Bad bearings Disassemble and or replace pump Pump sounds different No Yes Pump is moving some water No Replace pump Pump...

Страница 59: ...to outdoor sensor are OK Yes No Replace sensor OK now N06 notification message Outdoor sensor not present Check and tighten connections No Check the programming for Outdoor Reset Go to Installer Mode...

Страница 60: ...Select and Down buttons for 5 seconds to go to Installer mode 2 Use the Up and Down buttons to go to the setting you want to change P61 through P64 for Out door Reset 3 To make a change press the OK...

Страница 61: ...er condition Check water source See procedure below Green Amber Weak probe signal Clean probe or replace Low Water Cutoff See the procedure on the next page Red Amber Low water condition and weak prob...

Страница 62: ...water shutoff valves located upstream and downstream of the unit 3 Drain the boiler 4 Remove the upper front panel on the unit B19 cont 5 Disconnect the wires running to the front of the unit 6 Turn...

Страница 63: ...hanger is OK No Getting enough hot water Some hot water DHW setpoint is correct No Reset DHW setpoint P51 Yes No hot water Check DHW temp sensor Section B21 Check three way valve Section B23 Check DHW...

Страница 64: ...Use the main disconnect switch mounted on the front panel 2 Isolate the boiler Turn off the water shutoff valves located upstream and downstream of the unit 3 Drain the DHW piping 4 Remove the rear co...

Страница 65: ...ot water To test the sensor open a hot water faucet in the domestic water system The boiler should respond quickly If it does not the sensor may be bad Tools and equipment required Adjustable wrench o...

Страница 66: ...begins to send heat to the CH system and the timer set by P49 begins CH over DHW Normally the valve is operated by a solenoid controlled by the SIT board However the valve also includes a manual actua...

Страница 67: ...ion through the exchanger and revive it Laars recommends straight white vinegar for this purpose If this does not improve the performance the exchanger must be replaced Replacement Procedure The heat...

Страница 68: ...indirect tank is supplied by a loop off of the main central heat loop as shown in Fig B25 1 The DHW loop has its own DHW pump The control input can be provided by an aquastat see Sec tion B26 or a DH...

Страница 69: ...ough hot water Some hot water DHW setpoint is correct No Reset DHW setpoint P51 Yes No hot water Valves in DHW loop open Signal from aquastat at terminals 7 and 8 Check DHW pump Section B17 Check outl...

Страница 70: ...ction B17 DHW pump is OK No Getting enough hot water Some hot water DHW setpoint is correct No Reset DHW setpoint P51 Yes No hot water Valves in DHW loop open Check DHW pump Section B17 Replace SIT co...

Страница 71: ...ct to start the auto configuration process The controller will find all of the boilers connected to the system and assign Modbus addresses When the auto configuration is complete the display will say...

Страница 72: ...e at Maximum Voltage This is the default 0 10VDC configuration The external signal directly corresponds to fan speed or boiler power In this mode the call is initiated by the 0 10V input based on para...

Страница 73: ...by the controller itself Programs on the SIT Board and Display There are actually two copies of the program that controls this unit one copy in the display and an other copy in the SIT board If you re...

Страница 74: ...on them 8 The control board is supported on a set of six stand offs See Fig B30 3 The easiest way to release the board is to work with the lower part of each standoff first the part below or behind th...

Страница 75: ...or moisture Check for loose wires discoloration of parts leaks or any other signs of trouble Be sure to check the follow ing areas Control box Gas valve Sensors and switches Condensate trap Pump Thre...

Страница 76: ...70 Mascot LX Service Manual...

Страница 77: ...nding on the gas air mixture the burner can operate in three different ways When the burner is burning correctly correct gas and air mixture enough air is available to combine with the gas and the fla...

Страница 78: ...ts Remove the upper front panel so you can reach the gas valve shown in Fig C2 3 To adjust the high fire CO2 locate the high fire adjuster screw shown in Fig C2 3 Use the 2 5 mm Allen wrench Slowly ma...

Страница 79: ...CO2 is not correct repeat the steps listed above 7 Use the Down arrow to go back to 20 firing and re check the CO2 during Low Fire 8 Once the CO2 values are correct for both High Fire and Low Fire lea...

Страница 80: ...et pressure OK Yes No Gas supply problem Check with gas company Interior of burner is clean No Clean burner and heat exchanger See Section C4 Can reach Combustion is OK Replace gas valve See Section B...

Страница 81: ...he blower Black carbon soot buildup on a dirty heat exchanger can be ignited by a random spark or flame To prevent this from happening dampen the soot deposits with a wet brush or fine water spray bef...

Страница 82: ...xchanger 9 Once the tubes have been brushed clean rinse the tubes and combustion chamber In the gar den sprayer make a mixture of water with a small amount of white vinegar Use the sprayer to flush al...

Страница 83: ...rror E011 Lockout due to three consecutive flame losses during Run E012 Lockout due to three consecutive failed ignitions E013 Flue high temperature E014 Outlet high temperature manual reset high limi...

Страница 84: ...to flue gradient not detected n02 Fan speed limited due to outlet tempera ture n03 Fan speed limited due to Delta T inlet to outlet temperature difference n04 Fan speed limited due to flue tempera tur...

Страница 85: ...ime a bic must remain on or off 30 sec P12 Minimum next on time 60 sec P13 Maximum kBtu of this unit 125 P14 Maximum kBtu of Slave 1 0 P15 Maximum kBtu of Slave 2 0 P16 Maximum kBtu of Slave 3 0 P17 M...

Страница 86: ...for system pump 30 sec P42 Summer kick timer for central heat pump 20 sec P43 Summer kick timer for domestic hot water pump 20 sec P44 Summer kick timer for system pump 20 sec P45 Delta T setpoint fo...

Страница 87: ...rve HBT 180 F P63 High outdoor air temperature for heat curve HOD 70 F P64 Low setpoint for heat curve LBT 120 F P65 Outside temperature disabling central heat demand WWSD 90 F P66 Outside temperature...

Страница 88: ...ter the pre purge the direct spark and gas valve activate and the unit starts a four second trial for ignition 4 The unit fires and runs at a reduced rate of 45 for 10 seconds 5 After the reduced rate...

Страница 89: ...EUT NEUT NEUT LINE LINE LINE INTERLK T FIELD T GROUN D 2 1 2 1 4 2 BL 1 4 8 5 SENSOR OUTD OO R L1 IN NEUTRAL GROUND SYSTEM R W V V V BK G FRO M X5 BR TO FRO M X3 G Y BL G Y O R BK Y BL W 1 G Y W R R B...

Страница 90: ...84 Mascot LX Service Manual Appendix 3 Wiring Diagrams continued App3 cont Fig App3 2 120V Wiring Diagram...

Страница 91: ...l App3 cont Appendix 3 Wiring Diagrams continued High voltage field connections located behind the inside lower panel Low voltage field connections located on the front of the inside lower panel Fig A...

Страница 92: ...front cover or side of the unit 6 With a combustion analyzer check the CO2 levels at both maximum and minimum input See Section C2 Serious injury or death could occur if the CO2 levels are not adjuste...

Страница 93: ......

Страница 94: ...Rochester NH 03867 800 900 9276 603 335 6300 Fax 603 335 3355 1869 Sismet Road Mississauga Ontario Canada L4W 1W8 905 238 0100 Fax 905 366 0130 www Laars com Printed in U S A Laars Heating Systems 20...

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