High Limit Differential Setpoint Adjustment Procedure - A.O. Smith VB-500, VB-750 Instruction Manual

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)
The software revision level of the MCB.
• Current Error Screen:
Displays the last error that the system has detected plus a time
stamp of when the error occurred. (The time stamp is based
on the elapsed hours value at the time the error occurred. It
is displayed in hours and minutes. This error remain displayed
as long as it is 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.
NOTE: Errors are cleared from this screen by pressing
the "select" key.
• Error History Screen:
This screen displays a list of the last 9 errors (with time
stamps) that have occurred. The last error to occur
is displayed first. If a new error occurs this screen is
presented to display the error.
• Reload Defaults Screen:
From this screen the user can restore the factory default
values for screen adjustable configurations by pressing
the Select key. The values restored are as follows:
VW Models
Oper Setpnt (Operating Setpoint) - 145° F (63° C)
Hi Limit (High Limit Setpoint) = 210° F (99° C)
Hi Limit Dif (High Limit Differential) = 20° F (11° C)
VB Models
Oper Setpnt (Operating Setpoint) = 190° F (88° C)
Hi Limit (High Limit Setpoint) = 230° F (110° C)
Hi Limit Dif (High Limit Differential) = 20° F (11° C)
Both Models
Tempert Units (Temperature Units) = F
Post Cir Secs (Post Circulation pump delay = 45 seconds
Network Address (Network Address) = (none)
UIM Touch Switches
Below the LCD display are five touch switches or keys, that the
operator uses to operate the system.
• Menu Key:
Pressing this key activates the menu screen where the other
screens can be accessed.
• Select Key:
This key performs several functions. Screens can be selected
from the menu screen by pressing this key when the ">" appears
next to the screen desired.
On the User Settings screen items that appear next to a ">"
symbol can be selected with this key. If a setpoint configuration
item is selected, the ">" will then flash slowly to indicate that
the item has been selected. The Up and Down keys are then
used to change its value.
From the Current Error Screen this key is used to reset the
system from an error:
42