11
Common Settings
Stage 1, 2, 3, 4, 5, 6, 7, & 8 Auto or Off switch
When a stage switch is set to "Auto", that particular stage becomes active and its
boiler is available for operation. If the stage switch is "Off", the control will ignore that
stage and not turn it on.
Rotate switch
When this switch is set to "Rotate", the firing order of the stages is changed to even
out wear and tear on the boilers. Whenever one stage accumulates 48 hrs more
running time than the others, it will be rotated to be the last boiler fired and the boiler
with the least amount of running time will become the lead boiler. Whenever the Test
button is pushed, the control automatically re-ranks the firing sequence based on
accumulated running times. When the Rotate switch is set to "Off", the firing order will
always stay the same; 1,2,3,4,5,6,7,8 to stage on, and reverse order to stage off.
Fixed lead switch
When the boilers are to be rotated and this switch is set to "Fixed lead", the stages
are rotated as described above with the exception that Stage 1 will always be the first
boiler to fire and the first boiler to stage off. This feature is commonly used when a high
efficiency lead boiler is used in conjunction with mid efficiency boilers to increase
overall heating plant efficiencies, or when the boiler closest to a chimney needs to be
fired first in order to establish draft in the chimney.
Lo-Hi fire switch
When boilers are to be rotated and Lo-Hi fire boilers are used, the stages must be
rotated in such a way as to prevent possible High fire starts and mixing up of the stages
between boilers. When this switch is set to "Lo-Hi fire", the stages rotate as Lo-Hi fire
pairs (1 & 2 and 3 & 4, etc.) and the hours of use are calculated based on the Lo fire
run times. In addition, the control will not allow a Hi fire stage to operate if its
corresponding Lo fire stage DIP switch has been turned off. (ie. if Stage 1 is turned
off, stage 2 will not be allowed to fire and the control will move on to 3 & 4)
Fixed last switch
When the boilers are to be rotated and this switch is set to "Fixed last", the stages are
rotated as described above with the exception that Stage 8 will always be the last
boiler to fire and the first boiler to stage off. This feature is commonly used to operate
a diverting valve which will allow Domestic Hot Water boilers to be switched over to
assist the heating boilers during peak load times.
Int. timer switch
The 258 control has an internal timer – programmed using the LCD display and
keypad – that can be used to switch up to two Occupied/Unoccupied events per day
on a 7 day basis.
Details on the operation of this timer can be found in the "Programming" section on
page 15.
Ext. timer switch
The 258 control can be switched into the Unoccupied mode by an external signal
when a dry contact closure occurs between terminals
UnO Sw — Com Sen (26 & 28).
Minimum Supply Temperature
This dial should be set according to the requirements specified by the boiler
manufacturer. Many boilers require a minimum operating temperature to prevent
corrosion from flue gas condensation. The control raises the supply temperature to the
Minimum setting when the outdoor temperature drops below the WWSD point, and
holds it there until the outdoor temperature becomes cold enough to require operation
on the heating curve.
Note: Many boiler manufacturers requires a minimum return temperature to their
equipment. In systems where this is a strict requirement, the minimum supply
temperature setting should be set to the recommended return temperature plus the
boiler
∆
T under full load conditions.
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Auto
Stage
1 2 3 4 5 6 7 8
Perm.
Demand
Ext. timer
Fixed last
Int. timer
Lo-Hi fire
Fixed lead
Rotate
Off
1
2
3
4
5
6
7
8
9
External
Demand
Off
1
2
3
4
5
6
Stpnt
Reset
Minimum
120
°
F
Off
170
80