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Vitocrossal 300 CU3A 26 to 199 Service
Functional Description
Domestic hot water supply with gas-fired space heating
boiler
Domestic hot water heating is activated when the tank
temperature is 4.5ºF (2.5ºC) below the tank temperature
setpoint value. The burner and the tank DHW pump are
switched on. In the factory default setting, the desired
boiler water temperature is set at 36ºF (20ºC) above
the tank temperature setpoint value. When the actual
tank temperature rises 4.5ºF (2.5ºC) above the tank
temperature setpoint value, the burner is switched off
and the time delay function of the tank DHW pump is
activated.
The temperature differential of 4.5ºF (2.5ºC) can be
adjusted in coding level 2, address “59” DHW boost
heating / additional heating function. This function
will heat your DHW tank to a second DHW setpoint
temperature within the fourth time phase. It can act as
an “Anti-Legionnaire-Function” if the DHW supply is not
heated to 140ºF (60ºC) during the regular time schedule.
You can activate this function by selecting a switching
period for the fourth time phase. (See Operating
Instructions.)
The temperature setpoint for this function is adjustable in
coding address “58”.
Space heating mode
For operation with heating circuits the control unit
calculates a boiler water setpoint temperature based
on the outdoor or room temperature (where a room
temperature dependent remote control is connected) and
on the slope/shift of the heating curve.
The calculated boiler water setpoint temperature is
transmitted to the burner control unit.
For operation with zone circuits, the boiler water setpoint
operation temperature or calculated based on the slope/
shift of the heating curve.
From the boiler water setpoint and the actual temperature
the burner control calculates the degree of modulation
required, and regulates the burner accordingly. The
maximum operating boiler water temperature is limited in
the burner control unit to 194ºF (90ºC) by the electronic
temperature control.
The fixed high limits of the safety chain interlock
the burner control unit at 210ºF (99ºC) boiler water
temperature.
Service