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this state until the MCB sends a command to clear the error, 

and the system returns to the idle state.

•  Cold Purge State

  Cold  purge  occurs  when  the  MCB  micro  commands  the 

blower to go on before lighting to clear the unit of residual 

gases. This state normally lasts approximately 32 seconds 

but  on  a  special  situation  can  last  up  to  5  minutes.  If 

on  the  first  call  for  heat  after  power  up,  blower  prover 

switch is open, this state will take up to 5 minutes before 

declaring  an  error.

  The  MCB  will  wait  the  normal  cold  purge  time  (normally  32 

seconds)  before  checking  for  activation  of  all  active  blower 

prover.  If blower prover is active at this time the MCB cancels 

the cold purge request.  After the first cold purge has been done 

a flag is set to prevent further activation of the shutter adjust 

5 minute delay.  Any further requests for cold purge will last 

the normal cold purge time. The FCB will go into fault mode if 

the blower prover does not activate after 15 seconds. This time 

allows the blower relay to activate, the blower to come up to 

speed, and the response from the blower prover to be filtered.

•  User Settings Screen:

  Each setpoint or user setting has either a limited selection of 

values, or a limited range of values.  The Up/Down keys are 

used to change values.  After changing an item, the Select key 

is pressed to accept the change, or the Menu key is pressed 

to reject the change and restore the item to its original value.  

The following setpoints can be changed:

•  Operating Setpoint:

  This setpoint sets the base temperature for the control algorithm.

OPERATING SETPOINT ADJUSTMENT PROCEDURE

The  system  has  a  standard  programmable  Operating  Setpoint 

range  of  70°F  (21°C)  to  190°F  (88°C)  for  a  VW  and  of  70°F 

(21°C)  to  220°F  (104°C)  for  a  VB  for  either  a  Remote  or  inlet 

probe  depending  on  selection.  The  user  can  easily  change 

Operating Setpoint at any time by using the following procedure. 

When any configuration or setpoint is changed (and Select key 

touched),  new  value  is  IMMEDIATELY  saved  to  non-volatile 

memory. The factory default setting is 120°F (49°C).
1.  Press the MENU key.
2.  Scroll the “>” with the DOWN key next to the USER SETTING 

SCREEN.

3.  Press the SELECT key.
4.  Scroll  the  “>”  with  the  DOWN  key  until  it  is  pointing  to 

OPERATING SETPOINT.

5.  Press the SELECT key.
6.  Use the UP or DOWN key to select the value you wish to enter.
7.  Press the SELECT key to accept and store the new value.

•  High Limit:

  The outlet temperature probe contains both an MRHL switch 

and a thermistor for temperature measurement. The sensed 

outlet temperature is used for automatically resettable High Limit 

setpoint. If sensed outlet temperature exceeds High Limit setpoint, 

a “soft lockout” condition will occur and burner will be shut off. 

This fault condition is automatically cleared when  temperature 

drops below high limit setpoint minus high limit differential.

AUTO  HIGH  LIMIT  SETPOINT ADJUSTMENT  PROCEDURE/

OUTLET TEMPERATURE PROBE

The High Limit setpoint has a range of 90°F (32°C) to 210°F  (99°C) 

for a VW and a range of 90° (32°C) to 235°F (113°C) for a VB.  

Use the following procedure to change the automatically resettable 

High Limit Setpoint:

1.  Press the MENU key.

2.  Scroll the “>” with the DOWN key next to USER SETTING SCREEN.
3.  Press the SELECT key.
4.  Scroll the “>” with the DOWN key until it is pointing to HIGH 

LIMIT SETPOINT.

5.  Press the SELECT KEY.
6.  Use the UP and DOWN key to select the value you wish to enter.
7.  Press the SELECT key to accept and store the new value.

•  High Limit Differential:

  The outlet temperature must be below the automatic High Limit 

setpoint minus the High Limit Differential setpoint before  a call 

for heat can be generated.

HIGH  LIMIT  DIFFERENTIAL  SETPOINT  ADJUSTMENT 

PROCEDURE

The High Limit Differential Setpoint has a range of 1°F to 50°F for 

all models. Use the following procedure to change the High Limit 

Differential Setpoint:

1.  Press the MENU key.
2.  Scroll the “>” with the down key next to USER SETTING SCREEN.
3.  Press the SELECT key.
4.  Scroll the “>” with the DOWN key until it is pointing to HIGH LIMIT 

DIFFERENTIAL SETPOINT.

5.  Press the SELECT key.
6.  Use the UP or DOWN key to select the value you wish to enter.
7.  Press the SELECT key to accept and store the new value.

•  Operating  Differential  Setpoints:

  Each  of  the  two  stages  has  an  independent  Operating 

Differential  setpoint.

• 

Temperature  Units:

  Temperature  can  be  displayed  in  either  °F  or  °C  units.

• 

Post  Circulate  Delay  Time:

  The  time  circulation  pump  will  stay  on  after  the  burner 

is  turned  off.  The  time  in  seconds  is  adjustable  with 

the  following  values:  45,  90,  180  or  continuous.    If  the 

continuous  value  is  selected  the  pump  will  remain  on  at 

all  times  and  the  post  circulate  state  time  will  be  set  at 

45  seconds.

• 

Network Address:

  This is a unique number assigned to this boiler to differentiate 

it  from  other  boilers  or  water  heater  on  the  same  A.  O. 

Smith proprietary network. A valid Network Address can be 

any number from 1 to 31. It is set by default to zero, which 

is an invalid address. The boiler will not communicate until 

it is changed to a valid and unique number. This prevents 

two units from trying to respond to the same request from 

the  PC  or  supervisory  network  device.

• 

Configuration  Settings  Screen:

  Displays  the  status  of  the  dipswitches  installed  on  all 

boards  as  described  earlier.

• 

Log  &  System  Info  Screen:

  Displays  the  following  information:

  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)

  kBtu rating of the boiler (0 to 5750kBtu in 10kBtu increments)

Summary of Contents for VB 1500

Page 1: ...one in your building Immediately call your gas supplier from a neighbor s phone Follow the gas supplier s instructions If you cannot reach your gas supplier call the fire department Installation and s...

Page 2: ...ning Procedure Mechanical Removal of Deposits 22 Replacement Parts 22 LIMITED WARRANTY 23 TABLE OF CONTENTS 2 safe installation use and service 3 APPROVALS 3 GENERAL SAFETY 4 INTRODUCTION 5 INSTALLATI...

Page 3: ...hazardous situation which if not avoided could result in property damage WARNING CAUTION CAUTION DANGER All safety messages will generally tell you about the type of hazard what can happen if you do...

Page 4: ...etup and instructions before lighting Failure to implement the proper setup will result in improper and inefficient operation of the appliance resulting in production of increased levels of carbon mon...

Page 5: ...ion The installation must conform to all instructions contained in this manual and the local code authority having jurisdiction These should be carefully followed in all cases Authorities having juris...

Page 6: ...e horizontally vented gas fueled heating appliance or equipment The sign should read in print size no less than one half 1 2 inch in size GAS VENT DIRECTLY BELOW KEEP CLEAR OF ALL OBSTRUCTIONS INSPECT...

Page 7: ...DB F3 7 5 AMP FUSE MCB II F1 24VDC GENERATION MCB II K6 RELAY COIL MCB II MR HIGH LIMIT FLOW SWITCH LWCO SWITCH OPTIONAL LOW GAS SWITCH HIGH GAS SWITCH OPTIONAL EXTERNAL ENABLE OPTIONAL POWER ACC PROV...

Page 8: ...LE EXT ENABLE DISABLE COM NO COM NC NO COM COM NC ON OFF POWER RELAY NO COM G W W BK BK BK BK BK W 24VAC HOT W BK 24VAC RTN G GROUND F CAT 5 CABLE R G BK W MCB II DETAIL A Part of J BOX VB VW 1500 200...

Page 9: ...W UNITS COME EQUIPPED WITH PUMP VB UNITS DO NOT 24VAC COM PUMP RELAY A BK F 0 WIRING DIAGRAM TRANSFORMER 120 24 VAC MODULATING CONTROL BOARD II MCB II J20 or J21 J16 1 2 6 7 J24 F1 7 5A 24VAC J3 1 2 3...

Page 10: ...and permit pressure to be established by the pressure reducing valve 2 Vent all high points in system to purge system of air Provisions should be made to permit manual venting of radiators or convecto...

Page 11: ...water temperature or 20 F 11 C differential whichever has the higher inlet temperature is attained b If the inlet water temperature is greater than 120 F 49 C and the 20 F 11 C differential is not pre...

Page 12: ...12 LIGHTING AND OPERATING INSTRUCTIONS...

Page 13: ...efully adjust the low fire gas setting to achieve the CO2 level prescribed in above reference table Note The rotation of the Low Fire adjustment is opposite of the High Fire as follows Clockwise rotat...

Page 14: ...t will operate with the voltage and current level provided Pump MCB 120VAC required on systems that do not have an external pump Provides electrical power to directly operate a pump or the coil of an...

Page 15: ...idle state as displayed by the Standby LED The control will continue to monitor heat demand and state of other system devices Upon a drop of water temperature below the set parameters the control wil...

Page 16: ...when the fault state is exited Hard Fault State See Fault Description section for list of soft and Auto Reset faults The pump remains on for the selected post circulate time to cycle the hot water ou...

Page 17: ...soft lockout condition will occur and burner will be shut off This fault condition is automatically cleared when temperature drops below high limit setpoint minus high limit differential AUTO HIGH LI...

Page 18: ...nwards in screens to reach a desired item and to change setpoints and user settings They have an auto increment decrement feature for some of the configurations and values When you first press one of...

Page 19: ...the MCB and reading the resistance across the two active pinsontheconnectoratthe end of the probe cable The value should be approximately 0 ohms when the temperature of the probe is less than 220 F L...

Page 20: ...unction of the servo pressure regulator Replace the valve and add a gas filter in front of the new valve preventative maintenance This is a pre mix burner system The flame is not supposed to be direct...

Page 21: ...to move at this point FOR DIRECT VENT UNITS It is necessary to loosen and slide the rubber coupling on the blower adaptor in order to move the blower 4 Loosen the seven bolts on the blower adapter at...

Page 22: ...xist As the water is heated these tend to drop out depositing as scale or lime This scale must be removed before the heat exchanger tubes become blocked DELIMING The amount of calcium carbonate lime r...

Page 23: ...his boiler under state or provincial law are limited to one 1 year duration for the boiler or any of its parts Some states and provinces do not allow limitations on how long an implied warranty lasts...

Page 24: ...24 500 Tennessee Waltz Parkway Ashland City TN 37015 Technical Support 800 527 1953 Parts 800 433 2545 Fax 800 644 9306 www hotwater com...

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