Viessmann VITOTRONIC300 Installation And Service Instructions Manual page 79

Vitotronic 300, GW2B Installation and Service
Boiler Water Temperature Control
Boiler protection functions
Therm-Control
(Start-up system)
H For heating systems with distributor installed close
to the boiler.
H Requirement:
The boiler water flow rate in the startup phase
(e.g. after a weekend shutdown) must be able to be
reduced by at least 50%.
H Also affects the heating circuits of a Vitotronic 200-H
installed downstream.
Legend
sÖA1 Closing the mixing valves
Contactor relay
A
Downstream heating circuit controller, switching
B
contact closed:
Signal for mixing valve "Close"
(continued)
Function
The Therm-Control sensor, installed near the return
connector, captures the return temperature.
The burner is ramped up to full load if the factory-selected
set temperature (defaulted by the boiler coding card)
is not being achieved. The flow rate is reduced via the
mixing valve.
When the set temperature is exceeded, the mixing valves
are opened and the flow rate gradually increased to 100%.
Therm-Control in conjunction with heating systems that
are not connected with the Vitotronic via LON
Plug sÖA1 of the Vitotronic is used as switching contact
for the Therm-Control.
Required code: "4C:2" in the "General" group.
Raising the return temperature via a shunt pump
H For heating systems with distributor installed close to
the boiler.
H Requirement:
– The boiler water flow rate must be able to be reduced
by at least 50%.
– Shunt pump sized to approx. 30% of the total
throughput.
H Also affects the heating circuits of a Vitotronic 200-H
installed downstream.
Function
Temperature sensors T1 and T2 capture the return
temperature at different test points.
The shunt pump is started via temperature sensor T2
if the factory-selected minimum return temperature
(defaulted by the boiler coding card) is not being achieved.
The flow rate will be reduced via the mixing valve if the
minimum return temperature captured by temperature
sensor T1 is not achieved despite the return temperature
raising.
Function Description
79