Control Operations Guide Bosch Buderus SSB255 | SSB399 | SSB512 Boilers | 7
Bosch Thermotechnology Corp. | 03.2018
Data subject to change
Central Heating Mode 1
(On/Off with Outdoor Reset using dry contacts #11 and #12)
CH Mode “1” - Boiler demand is generated thru a call for heat on low voltage
contacts #11 and #12 (dry contacts only). Boiler will target a system supply water
temperature equal to the corresponding point on the installer programmed heating
curve. (See page 7 for details on how-to program the heating curve). If the System
Temperature sensor exceeds the calculated heating curve temperature by “CH
Hysteresis” (par.#7) the burner will shut off until the System Temperature sensor
reads “CH Hysteresis” below the target Setpoint Temperature.
Example:
Based on the heating curve programmed by the installer, the calculated supply water
temperature on a 32°F degree day outside corresponds with a target boiler water
temperature of 140°F. If CH Hysteresis is set for 10°F, and there is a call for heat
on #11 and #12, then the burner will turn on when the Boiler Supply Temperature
sensor (System Supply Temperature sensor for cascade) reads a temperture of
130°F or less and will remain operating until the call for heat is satisifi ed or until the
sensor reads a temperature of 150°F or greater. As long as the call for heat remains
the Boiler and CH Pump contacts will remain energized. The Burner will remain off
until temperature measured at the system supply sensor falls to 130°F
Central Heating
(CH) Mode
Description
Set these Parameters
Parameter # Description Default Range
CH Mode = “1”
On/Off with reset water
temperature
19 Design Supply °F 176°F 68 - 194°F
20 Design Outdoor °F 24.8°F -13 - 77°F
21 Baseline Supply °F 104°F 68 - 194°F
22 Baseline Outdoor °F 69.8°F 35.6 - 86°F
23 Design Supply min 68°F 39.2 – 179.6°F
24 Design Supply max 194°F 80.6 - 194°F
25 WWSD 69.8°F 35.6 - 95°F
26 Boost Temp Incr. 0°F 0 - 54°F
27 Boost Temp Delay 20 min. 1 – 120 min.
Table 3
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