Viessmann Vitotwin 300-W Installation And Service Instructions For Contractors page 155

Boiler temperature control
Oil/gas boilers as auxiliary heat sources
See system version 3.
The auxiliary heat source is controlled
via the set flow temperature for the heat-
ing circuits. It is enabled via terminal
QX4 on Vitotwin 300-W at the external
hook-up for the boiler and heating circuit
control unit. It is only enabled if the out-
put of Vitotwin 300-W exceeds the value
set in coding address 3691 (delivered
condition 80 %) or the actual flow tem-
perature falls sharply.
The auxiliary heat source can be locked
in a selected outside temperature range
via codes 3700 and 3701 (delivered con-
dition "- - -", auxiliary heat source always
enabled or no restriction).
The auxiliary heat source can be started
with a time delay on demand via code
3723 (delivered condition "- - -", function
switched off).
If the type of auxiliary heat source has
been selected via code 3750, this is dis-
played accordingly.
If economy mode is switched on, the
auxiliary heat source is locked in the
delivered condition (code 3702).
Solid fuel boiler as auxiliary heat source
See system version 4.
The additional buffer cylinder is connec-
ted via the Vitosolic (ΔT-control).
(cont.)
■ Starting criterion:
If the actual flow temperature on the
common flow temperature sensor
(common flow sensor B10) falls below
the set flow temperature by
the"Switching diff on", the diverter
valve (terminal QX2) switches and
passes through the boiler. The auxili-
ary heat source burner is enabled if the
"Switching integral" (code 3720) is
reached.
When the auxiliary heat source is ena-
bled, the set flow temperature for
Vitotwin 300-W is increased by 10 K
(code 3690), so that this is not
switched off or modulated.
■ Shutdown criterion:
Burner enable will be blocked if the
actual flow temperature on the com-
mon flow temperature sensor (com-
mon flow sensor B10) rises above the
set flow temperature by the "Switch-
ing diff off" (code 3722). The diverter
valve is switched once the run-on time
has elapsed.
Auxiliary heating source and DHW
heating
The auxiliary heat source is only enabled
for DHW heating if the Vitotwin 300-W
cannot be operated (code 3692), e.g. as
a result of a fault.
Code 5982 must be selected as "Supp
burner block" and code 5891 as "DHW
ctrl elem Q3".
Function description
155