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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)
