Viessmann FB2B Installation And Service Instructions Manual page 128

Function description
Control unit
(cont.)
The primary cylinder is heated up to the
set DHW temperature. Heating stops
when the set temperatures have been
reached at the cylinder temperature sen-
sor and at the outlet temperature sen-
sor.
Boosting when DHW is drawn off
When DHW is drawn off, cold water
enters at the bottom of the primary cyl-
inder.
The heating circuit pump is switched ON
and the three-way diverter valve is
changed over, if the cylinder tempera-
ture sensor recognises a temperature
lower than the set temperature.
■ The cylinder primary pump is switched
ON if the boiler water temperature ≥
set DHW temperature.
■ The burner is switched ON if the boiler
water temperature ≤ set DHW temper-
ature, and the cylinder primary pump
is switched ON when the required
boiler water temperature is reached.
DHW heating via solar collectors
If a temperature differential is measured
between the collector temperature sen-
sor and the cylinder temperature sensor
of the solar control module, which is
greater than the start temperature differ-
ential set in the control unit, the solar cir-
cuit pump is started and the DHW cylin-
der is heated.
128
After heating, the cylinder primary pump
and the three-way diverter valve remain
ON for a further 30 s.
The DHW is controlled to the specified
temperature via the cylinder temperature
sensor.
The primary cylinder continues to be
heated up after the draw off process has
terminated, until the set DHW tempera-
ture has been reached at the cylinder
temperature sensor.
The cylinder primary pump and the
three-way diverter valve remain ON for a
further 30 s.
The pump is stopped if the temperature
falls below the stop temperature differ-
ential between the collector temperature
sensor and the cylinder temperature
sensor of the solar control module.
The solar circuit pump is stopped if the
set maximum temperature or the tem-
perature set at the temperature limiter is
reached.