Vulcan-Hart MHB24G Service Manual
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Vulcan-Hart MHB24G Service Manual

Vhx boiler base series high efficiency gas steamers
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See also: Operation & Installation Manual
VHX24G SHOWN
This Manual is prepared for the use of trained Vulcan Service
Technicians and should not be used by those not properly
qualified. If you have attended a Vulcan Service School for this
product, you may be qualified to perform all the procedures
described in this manual.
This manual is not intended to be all encompassing. If you have
not attended a Vulcan Service School for this product, you should
read, in its entirety, the repair procedure you wish to perform to
determine if you have the necessary tools, instruments and skills
required to perform the procedure. Procedures for which you do
not have the necessary tools, instruments and skills should be
performed by a trained Vulcan Service Technician.
Reproduction or other use of this Manual, without the express
written consent of Vulcan, is prohibited.
A product of VULCAN-HART
SERVICE MANUAL
VHX BOILER BASE SERIES
HIGH EFFICIENCY GAS
STEAMERS
VHX24G
ML-114795
VHX24G5
ML-126590
MHB24G
ML-114954 (BASE ONLY)
- NOTICE -
LOUISVILLE, KY 40201-0696
F24700 (October 2001)

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Summary of Contents for Vulcan-Hart MHB24G

  • Page 1 Vulcan Service Technician. Reproduction or other use of this Manual, without the express written consent of Vulcan, is prohibited. A product of VULCAN-HART SERVICE MANUAL VHX BOILER BASE SERIES HIGH EFFICIENCY GAS...

  • Page 2: Table Of Contents

    TABLE OF CONTENTS GENERAL ................4 Installation .
  • Page 3 Air Pressure Switch Adjustment ............33 Gas Pilot Pressure Adjustment .

  • Page 4: General

    Pan Size 12" x 20" F24700 (October 2001) GENERAL Model Designations Boiler Code Descriptions Vulcan-Hart incorporates redundant controls in compliance with the CSD-1 controls and safety devices for boiler construction on these High Efficiency Steam models. A Description of the code is listed below.

  • Page 5: Boiler Control Styles

    VHX SERIES STEAMERS - GENERAL Boiler Control Styles VHX Steamers manufactured using the old style boiler controls ended on 5/19/00. Steamers that were in stock at the time of the boiler control changeover were removed and equipped with the new style controls without recording the serial number for tracking.

  • Page 6: Water Conditioning

    WATER CONDITIONING Furnishing the boiler with treated water to reduce scale formation is important. Scale formation will reduce steam output, cause premature component failure, and shorten equipment life. Most water supplies contain scale producing minerals such as Calcium and Magnesium. As steam is generated, the minerals remain and dissolve into the water.

  • Page 7: Gas Supply

    200,000 200,000 VHX24G5 270,000 270,000 200,000 200,000 MHB24G 270,000 270,000 1. Output Boiler Horsepower (BHP): 4.3 BHP for 200,000 BTU; 5.5 BHP for 270,000 BTU. NOTE: 2. Input BTU/HR difference is based on gas orifice size and air orifice size.

  • Page 8: Steamer Operation

    STEAMER OPERATION CABINET BASE BOILER Ensure that all utility connections to the steamer have been made and are turned ON and that the knob on the main gas valve is in the ON position. The VHX Series steamers are CSD-1 compliant and are equipped with amber colored lights on the boiler control panel for High Pressure and Low Water level that illuminate and stay on until the boiler is full and...

  • Page 9: Boiler Blowdown And Steamer Shut Off

    With both timer knobs at the off position, open the compartment doors and observe that no steam has entered the cooking compartments, then close the doors. Set both timer knobs at 2 minutes. The ready lights will go off, the cooking lights will come on, and steam will begin to enter the compartments.

  • Page 10: Component Function

    COMPONENT FUNCTION CABINET BASE BOILER CONTROLS Power Switch (ON/OFF) ..When turned ON, supplies power to the control circuit. Reset Switch (Manual) ..Resets the low water level safety circuit on initial startup or the Boiler Fill Solenoid Valve .
  • Page 11 Relay Board ....Provides a centralized location for wire harness connections and power NOTE: The relay’s below are mounted on the relay board and are not individually replaceable. K1 Relay .

  • Page 12: Cooking Compartment Controls

    COOKING COMPARTMENT CONTROLS The upper section of the steamer consists of two separate cooking compartments. Each compartment functions independently with its own set of controls. Power is supplied to the controls only after the steam pressure rises above the compartment pressure switch setting to close the N.O. contacts. Ready Light (Green) .

  • Page 13: Removal And Replacement Of Parts

    VHX SERIES STEAMERS - REMOVAL AND REPLACEMENT OF PARTS REMOVAL AND REPLACEMENT OF PARTS COMPONENT LOCATIONS Cabinet Base Boiler Controls Page 13 of 68 F24700 (October 2001)
  • Page 14 VHX SERIES STEAMERS - REMOVAL AND REPLACEMENT OF PARTS Cabinet Base Boiler Controls Continued F24700 (October 2001) Page 14 of 68...

  • Page 15: Cooking Compartment Controls

    Cooking Compartment Controls WATER LEVEL CONTROLS (MAIN OR AUXILIARY LLCO) WARNING: DISCONNECT THE ELECTRICAL POWER TO THE MACHINE AT THE MAIN CIRCUIT BOX. PLACE A TAG ON THE CIRCUIT BOX INDICATING THE CIRCUIT IS BEING SERVICED. Open the cabinet base door. Remove the cover from the pressure switch control box to access the water level controls.

  • Page 16: Water Level Gauge Assembly

    WATER LEVEL GAUGE ASSEMBLY WARNING: DISCONNECT THE ELECTRICAL POWER TO THE MACHINE AT THE MAIN CIRCUIT BOX. PLACE A TAG ON THE CIRCUIT BOX INDICATING THE CIRCUIT IS BEING SERVICED. Open the cabinet base door and remove the right side panel. Close the valve at the top and at the bottom of the gauge assembly.

  • Page 17: Boiler Fill And Cold Water Condenser Solenoid Valves

    From the bottom right side, raise the boiler two to three inches so it tilts to the left. When the remaining water has drained out, lower the boiler before. proceeding. Remove the drain/scale clean-out plug from the bottom of the boiler. Slide the boiler forward and remove it from base frame.

  • Page 18: Burner Head Assembly

    BURNER HEAD ASSEMBLY WARNING: DISCONNECT THE ELECTRICAL POWER TO THE MACHINE AT THE MAIN CIRCUIT BOX. PLACE A TAG ON THE CIRCUIT BOX INDICATING THE CIRCUIT IS BEING SERVICED. WARNING: SHUT OFF THE GAS SUPPLY BEFORE SERVICING THE UNIT. Remove the pressure gauge tubing and power cable from the rear of the control panel then remove the panel.

  • Page 19: Heat Exchanger

    HEAT EXCHANGER WARNING: SHUT OFF THE GAS BEFORE SERVICING THE UNIT. WARNING: ALL GAS JOINTS DISTURBED DURING SERVICING MUST BE CHECKED FOR LEAKS. CHECK WITH A SOAP AND WATER SOLUTION (BUBBLES). DO NOT USE AN OPEN FLAME. Blowdown the boiler and, if necessary, allow to cool.
  • Page 20 12. For clearance of the heat exchanger only, remove the drain nut (petcock) and the lower adjustment knob from the water level gauge. Remove the remaining bolts on the heat exchanger then pull heat exchanger straight out from the boiler. F24700 (October 2001) 13.

  • Page 21: Cooking Compartment Door(S)

    NOTE: It may be necessary to use two clamps to draw the bottom of the heat exchanger close enough to be clamped. Start one clamp at a 3 o’clock position then install other clamp near the bottom. Once the bolts are tight enough, C- Clamp will fall away.
  • Page 22 Handle Open the door. Remove screws from the top and bottom of the door. Pull the inner door panel out from the door housing with the gasket plate and gasket still attached. Remove the nuts and spacers from the handle screws and remove the handle from the door.

  • Page 23: Service Procedures And Adjustments

    SERVICE PROCEDURES AND ADJUSTMENTS WARNING: CERTAIN PROCEDURES IN THIS SECTION REQUIRES ELECTRICAL TEST OR MEASUREMENTS WHILE POWER IS APPLIED TO THE MACHINE. EXERCISE EXTREME CAUTION AT ALL TIMES. IF TEST POINTS ARE NOT EASILY ACCESSIBLE, DISCONNECT POWER, ATTACH TEST EQUIPMENT AND REAPPLY POWER TO TEST. BOILER Inspection It is recommended the boiler be inspected for...

  • Page 24: Descaler (Cathodic Protector)

    WARNING: READ AND FOLLOW THE INSTRUCTIONS FOR THE DE-LIMING CHEMICAL BEING USED. USE PLASTIC OR RUBBER GLOVES TO AVOID SKIN CONTACT. IF THE CHEMICAL COMES IN CONTACT WITH SKIN, RINSE WITH CLEAN WATER. Mix deliming solution according to the instructions for the chemical being used. NOTE: Boiler water capacity is approximately seven gallons.

  • Page 25: Water Level Controls Test

    used, a frequent interval should be used. This blowdown procedure is essential to proper operation and component life by removing sediment and scalants that may be lodged in the probe housing. NOTE: Boiler should be within normal operating pressures. Remove the left side boiler base panel to access the ball valve.
  • Page 26 Verify LED’s on the water level control board, HL LED should be off, and LLCO LED should be illuminated. Open the ball valve in the probe housing assembly (boiler left side) about half way, to gradually remove boiler water and activate a fill cycle.

  • Page 27: Pressure Switches

    boiler shell, remove and clean the Aux LLCO probe. Replace the probe and check resistance again. If resistance is still present, install a new probe. Replace lead wire on probe and repeat steps "2) thru 4)" to verify proper operation. PRESSURE SWITCHES WARNING: THE FOLLOWING STEPS REQUIRE POWER TO BE APPLIED TO THE UNIT DURING...

  • Page 28: Fill And Cold Water Solenoid Valves

    Mechanical Pressure relief valve factory set to approximately 15 PSI. If the pressure in the boiler reaches this level, the valve will OPEN. High pressure light (amber) will come ON. If the pressure switch opens at a pressure range other than 14.5 to 15.0 PSI then an adjustment to the switch setting should be made.

  • Page 29: Boiler Blowdown/Drain Solenoid Valve

    Check ports in valve body. Reverse procedure to install. BOILER BLOWDOWN/DRAIN SOLENOID VALVE The water contained in the boiler, being under pressure, should be "blown through" this valve and be noticeably visible exhausting out the steamer drain. Daily boiler blowdown is essential to proper operation and component life by removing sediment and scalants that may be lodged in the chamber of the boiler.

  • Page 30: Main Burner Ignition Checks

    MAIN BURNER IGNITION CHECKS The complete gas burner assembly is located inside the heat exchanger casting in the boiler. The perforated burner head functions as both pilot and main gas burner. The inner portion of the perforated burner head serves as the pilot to light the main burner during the trial for ignition.
  • Page 31 If ignitor sparks and pilot lights, proceed to step 7. If ignitor does not spark, proceed to step "5)" below. Restart power ON sequence by "rapidly" turning the power switch OFF then back ON. A rapid switching is needed to keep the boiler from starting automatic blowdown.
  • Page 32 VHX SERIES STEAMER - SERVICE PROCEDURES AND ADJUSTMENTS F24700 (October 2001) Page 32 of 68...

  • Page 33: Air Pressure Switch Adjustment

    AIR PRESSURE SWITCH ADJUSTMENT The air pressure switch senses the pressure level produced by the blower for combustion. When the pressure is sufficient, the switch closes and supplies power to the ignition control module. The gas ignition sequence starts to light the gas pilot and then main burner.

  • Page 34: Gas Pilot Pressure Adjustment

    Replace the orifice, pressure switch and connect the lead wires to the switch. Turn the power switch ON and adjust the pressure switch again as outlined in steps 4A and 4B. Verify the pilot gas valve is energizing. If the pilot gas valve is not energizing and power is available to the pressure switch, turn the power switch OFF.
  • Page 35 After the main burner lights, allow the boiler to reach operating pressure then turn the ON/OFF knob for the main gas valve to OFF. Restart the ignition sequence by "rapidly" turning the power switch OFF then back ON. A rapid switching is needed to keep the boiler from starting automatic blowdown.

  • Page 36: Gas Manifold Pressure Adjustment

    GAS MANIFOLD PRESSURE ADJUSTMENT WARNING: DISCONNECT THE ELECTRICAL POWER TO THE MACHINE AT THE MAIN CIRCUIT BOX. PLACE A TAG ON THE CIRCUIT BOX INDICATING THE CIRCUIT IS BEING SERVICED. WARNING: SHUT OFF THE GAS SUPPLY BEFORE SERVICING THE UNIT. Open the cabinet base door to access main gas valve.

  • Page 37: Ignition Control Module Checks

    Once the correct pressure has been set, turn the gas supply and power switch OFF. Replace the adjustment screw cap and manifold pressure plug tap plug on the valve. Turn the gas supply on and check for proper operation. IGNITION CONTROL MODULE CHECKS Turn the power switch ON and allow the boiler to fill.
  • Page 38 Spark Verification Test Turn the power switch OFF. Check to ensure that all electrical terminal connections on the ignition control module and the ignitor rod are clean and tight. If the ignition cable appears to be damaged, replace it and re-try lighting burner.

  • Page 39: Cooking Compartment

    COOKING COMPARTMENT NOTE: For access to compartment controls, remove the right side compartment panel. Intake Shut-Off Valve Adjustment (Steam Flow) With the right side compartment panel removed, open the intake shut-off valve completely. If the steamer ready light is on, then proceed to step 4.

  • Page 40: Door Latch Adjustment

    Door Latch Adjustment Should the cooker door jam and can not be opened, DO NOT FORCE OR PRY the door as damage will occur. First, try lifting up on the bottom of the door at the handle end to disengage the latch. If that does not work, remove the right side panel.

  • Page 41: Electrical Operation

    ELECTRICAL OPERATION WATER LEVEL CONTROLS Low Level Cut-Off & Differential Control The steamer is equipped with three water level sensing probes (high, low and low level cut-off) and a single water level control board (solid state). The water level control board performs two functions: 1) Provide low level cut-off protection to shut off the heat source in case the water level drops below the low level cut-off (LLCO) probe.

  • Page 42: Auxiliary Low Level Cut-Off

    VHX SERIES STEAMER - ELECTRICAL OPERATION Auxiliary Low Level Cut-Off This control serves as a safety backup to the main water level control (WLC) board to meet CSD-1 code requirements. The operation of the auxiliary control is identical to the low level cut-off (LLCO) function of the main WLC board but performs a single function: 1) Provide auxiliary low level cut-off protection to shut off the heat source in case the...

  • Page 43: Relay Board

    RELAY BOARD Board Layout and LED Legend The relay board Provides a centralized location for wire harness connections and power transfer through board relays (K1-K7) to the other steamer controls. Also, provides a condition or component troubleshooting indicator by utilizing seventeen LED’S on the board to represent the status of the condition or component in the operating sequence.

  • Page 44: Boiler Operational Status (Led Indicator)

    Boiler Operational Status (LED Indicator) Use the tables below to determine the operational status of a component or condition by utilizing the LED indicators on the board. The operational state’s are divided into categories A thru F. Initial Conditions: (STATE A) - 120V, water and gas supplied to steamer - Power Switch ON - HIGH PRESS and LOW WATER lights ON (amber, front control panel)
  • Page 45 STATUS same as “state A” same as "state B" same as “state A” same as "state B Reset switch is/was momentarily energized Aux Water level is satisfied. (Amber WATER light OFF) Reset switch is/was momentarily energized High Limit is satisfied. (Amber HIGH PRESS OFF) same as “state A”...

  • Page 46: Sequence Of Operation

    SEQUENCE OF OPERATION NEW STYLE CONTROLS - BOILER This sequence of operation is written for boiler bases with the new style boiler controls. See "BOILER CONTROL STYLES" under "GENERAL". Refer to schematic diagram TSP1480. Initial Fill and Preheat Conditions. Power switch OFF. Boiler connected to correct voltage (120VAC).
  • Page 47 NOTE: Relay K4 remains energized through K4(1) N.O. locking circuit. N8 goes out. K4(1) N.O. contacts close and K4(1) N.C. contacts open. High pressure light (control panel) goes out. N11 lit. K4(2) N.O. contacts close. K5 is energized (24VAC). N12 lit. K5(1) N.O. contacts close.

  • Page 48: Old Style Controls - Boiler

    upper and lower set point limits. The cycling pressure switch continues to energize and de-energize the heating circuit to cycle the burner ON and OFF. This sequence continues until one of the following occurs: Power switch is turned OFF. Boiler water level drops below the LLCO probes for the main water level control (WLC) and the auxiliary low level control.
  • Page 49 Water level reaches LLCO (low water level cut- off) probe for the water level control and to the auxiliary LLCO probe for the auxiliary low level cut-off control. LLCO relay energizes, LLCO contacts (N.O.) CLOSE and LED lights. NOTE: No power is transferred until ignition sequence starts.

  • Page 50: Cooking Compartment Controls

    upper and lower set point limits. The cycling pressure switch continues to energize and de-energize the heating circuit to cycle the burner ON and OFF. This sequence continues until one of the following occurs: Power switch is turned OFF. Boiler water level drops below the LLCO probes for the main water level control and the auxiliary low level cut- off control...
  • Page 51 VHX SERIES STEAMER - ELECTRICAL OPERATION - THIS PAGE INTENTIONALLY LEFT BLANK - Page 51 of 68 F24700 (October 2001)

  • Page 52: Schematics

    VHX SERIES STEAMER - ELECTRICAL OPERATION SCHEMATICS Models Built After 5/25/00 (New Style Boiler Controls) F24700 (October 2001) Page 52 of 68...
  • Page 53 VHX SERIES STEAMER - ELECTRICAL OPERATION Page 53 of 68 F24700 (October 2001)

  • Page 54: Models Built Before 5/25/00 (Old Style Boiler Controls)

    VHX SERIES STEAMER - ELECTRICAL OPERATION Models Built Before 5/25/00 (Old Style Boiler Controls) F24700 (October 2001) Page 54 of 68...

  • Page 55: Cooking Compartment Controls

    VHX SERIES STEAMER - ELECTRICAL OPERATION Cooking Compartment Controls Page 55 of 68 F24700 (October 2001)

  • Page 56: Wiring Diagrams

    VHX SERIES STEAMER - ELECTRICAL OPERATION WIRING DIAGRAMS Models Built After 5/25/00 (New Style Boiler Controls) F24700 (October 2001) Page 56 of 68...
  • Page 57 VHX SERIES STEAMER - ELECTRICAL OPERATION Page 57 of 68 F24700 (October 2001)

  • Page 58: Models Built Before 5/25/00 (Old Style Boiler Controls)

    VHX SERIES STEAMER - ELECTRICAL OPERATION Models Built Before 5/25/00 (Old Style Boiler Controls) F24700 (October 2001) Page 58 of 68...
  • Page 59 VHX SERIES STEAMER - ELECTRICAL OPERATION Page 59 of 68 F24700 (October 2001)

  • Page 60: Cooking Compartment Controls

    VHX SERIES STEAMER - ELECTRICAL OPERATION Cooking Compartment Controls F24700 (October 2001) Page 60 of 68...

  • Page 61: Troubleshooting

    WARNING: CERTAIN PROCEDURES IN THIS SECTION REQUIRE ELECTRICAL TESTS OR MEASUREMENTS WHILE POWER IS APPLIED TO THE MACHINE. EXERCISE EXTREME CAUTION AT ALL TIMES. IF TEST POINTS ARE NOT EASILY ACCESSIBLE, DISCONNECT POWER, ATTACH TEST EQUIPMENT AND REAPPLY POWER TO TEST. Models with new style controls: Before performing any of the troubleshooting checks listed below, remove the cover from the main control box and check the condition of the LED’S on the relay board for the status of the condition or component in the operating sequence.
  • Page 62 SYMPTOM Blower operating, no pilot gas flow. Pilot flame not proving or lighting main burner. Main burner not lighting correctly or excessive ignition noise. Excess combustion noise or combustion induced harmonics. Boiler not maintaining set pressure and/or excessive burner on time. F24700 (October 2001) POSSIBLE CAUSES 1.
  • Page 63 SYMPTOM Gas odor. Drain box leaking. Cold water condenser not operating properly. Heat coming on without water in boiler (Dry firing). Spark Ignitor not sparking. POSSIBLE CAUSES 1. Leaks in pipe fitting connections or components. 2. Leaking pressure tap plug on pilot or main gas valve; loose or missing pressure adjustment screw cap on main gas valve.
  • Page 64 SYMPTOM Boiler Slow to Pressurize (over 15 min. to achieve operating pressure) Boiler will not heat or build pressure. Pressure relief valve(s) opening or leaking. F24700 (October 2001) POSSIBLE CAUSES 1. Low water supply pressure, inline water strainer clogged or fill solenoid valve malfunction.
  • Page 65 SYMPTOM Steam output low or slow cooking. Steamer leaks water. Boiler water level too high. Boiler does not fill. Burner won’t light. POSSIBLE CAUSES 1. Cooking Compartment. A. Blocked steam injector ports. (Open door, press door switch button and verify good steam flow into compartment).

  • Page 66: Cooking Compartment Controls

    COOKING COMPARTMENT CONTROLS SYMPTOM Cooking compartments do not operate. Steam generated inside compartment when timer is off. Timer motor does not run. Door not closing properly. Door won’t open. Buzzer not operating. Compartment leaks water around door or water accumulating in compartment . Steam leaks around door.
  • Page 67 VHX SERIES STEAMER - NOTES - Page 67 of 68 F24700 (October 2001)

  • Page 68: Condensed Spare Parts List

    Power Cord, drain Valve 844130-3 Cable, Ignitor 18" 853275-1 Switch assembly, on/off, reset & lights 853273-1 Relay Board 411690-1 Timer, Cooking 843836 Steam Solenoid Valves, Cooking Compartment F24700 (October 2001) NEW STYLE CONTROLS ONLY VHX24G, VHX24G5, MHB24G DESCRIPTION NOTES Printed in U.S.A.

This manual is also suitable for:

Vhx24gVhx24g5Ml-114795Ml-126590Ml-114954

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