Control Operations Guide
Bosch Buderus SSB255 | SSB399 | SSB512 Boilers
| 9
Bosch Thermotechnology Corp.
|
03.2018
Data subject to change
Central Heating Mode 3
(Permanent set point demand)
CH Mode“3”
- Boiler demand is always “ON” in CH Mode 3 – “Permanent Demand
Mode”. In this mode the Boiler and CH Pump contacts will always be energized. When
the Supply Temperature Sensor falls below the value of “
CH Setpoint
” (par.#3)
minus the value of “
CH Hysteresis
” (par.#7), the burner will turn on. The burner
will remain on as long as the supply temperature remains below the value of “CH
Setpoint” plus “CH Hysteresis”. Using the low voltage contacts #11 and #12 it is
possible to apply a set-back to the “CH Setpoint” target temperature. “
Night Setback
Dif
” (par.# 28) controls the temperature shift that is applied to the “CH Setpoint”
when #11 and #12 contacts are “closed” using a clock or switch.
Example:
With both Boiler and CH Pump contacts energized, the boiler will monitor the Supply
Temperature Sensor. The application calls for a setpoint of 140°F with and Hysteresis
setting of 10°F. When the temperature of the Boiler Supply Temperature sensor
(System Supply Temperature sensor for cascade) falls below 130°F ( the value of
“CH Setpoint” minus “CH Hysteresis”) the burners will turn on. Burners will remain
on as long as the sensor does not exceed 150°F ( the value of “CH Setpoint” plus
“CH Hysteresis”). In the evening the application calls for a reduced supply water
temperature of 120°F. A timer/clock is installed and wired to contacts #11 and #12
of the boiler and these contacts are “closed” between the hours of 10 pm and 5 am.
During that time period the “CH Setpoint” is reduced by the value programmed into
“Night Setback Dif”. In this example the value is set for 20°F.
Central Heating
(CH) Mode
Description
Set these Parameters
Parameter #
Description
Default
Range
CH Mode = “3”
Permanent
Setpoint
Demand
3
CH Setpoint
176°F
68 - 194°F
4
System pump overrun
300 sec.
0 – 900 sec.
5
Boiler pump overrun
300 sec.
0 – 900 sec.
7
CH Hysteresis
5.4°F
9
Anti-cycle period
180 sec.
10 – 900 sec.
10
Anti-cycle Temp Diff
12.6°F
0 - 36°F
24
Setpoint Max.
194°F
80.6 - 194°F
28
Night Setback
18°F
0 - 90°F
Table 5
