Viessmann VITOTRONIC 200 Service Instructions Manual page 20

Function description
Booster heaters
Connect two high limit safety cut-outs
(switching threshold respectively 70 °C)
for protection against excessively high
heat pump flow and return temperatures:
■ High limit safety cut-out for switching
off the external heat source
and
■ High limit safety cut-out for switching
off the secondary pumps
Instantaneous heating water heater
An electric instantaneous heating water
heater can be integrated in the secon-
dary circuit flow as an auxiliary heat
source.
Subject to the type of heat pump, the
instantaneous heating water heater can
be part of the standard delivery, an
accessory, or need to be supplied on
site.
Installation instructions, instanta-
neous heating water heater
The instantaneous heating water heater
can be enabled separately for central
heating and DHW reheating. For central
heating with an instantaneous heating
water heater, the long term average out-
side temperature must be below the
"Dual mode temp. instant. heating
water heater 790B".
Subject to the heat demand, the heat
pump control unit switches on stages 1,
2 or 3 of the instantaneous heating water
heater ("Max. output instantaneous
heating water heater 7907"). As soon
as the max. flow temperature for the sec-
ondary circuit "Max. flow temperature
heating circuit 200E" is reached, the
heat pump control unit stops the instan-
taneous heating water heater.
20
(cont.)
To limit the total power consumption, the
heat pump control unit stops the instan-
taneous heating water heater for a few
seconds directly before the compressor
starts. Each stage is subsequently star-
ted individually one after the other in
intervals of 10 s.
If the instantaneous heating water heater
is on and the differential between flow
and return temperatures in the secon-
dary circuit does not rise by at least 1 K
within 24 h, the heat pump control unit
displays the fault message "AB
Instant.htg wtr heater".