Viessmann SCU345 Manual page 67

Tanks cool down at night.
Collector circuit pump runs during the night?
no
Check controller
Collector temperature at night is higher than the
outdoor temperature.
no
Check the non-return valves
in the flow and the return pipe
for functional efficiency.
Sufficient tank insulation?
yes
Increase insulation.
Insulation close enough to the tank?
yes
Replace insulation or
increase it.
Are the tank connections insulated?
yes
Insulate the connections.
a
a
Warm water outflow upwards?
no
yes
yes
Does the warm water circulation run for a very
long time?
no
no
Circulation pump and blocking valve should
be switched off for 1 night; less tank losses?
no
yes
no
a
yes
Change connection and let
the water flow sidewards or
through a siphon (down-
wards); less tank losses now?
no yes
o.k.
yes
Use the circulation pump
with timer and switch-off
thermostat (energy efficient
circulation).
no
Check whether the pumps
of the after-heating circuit
run at night; check whether
the non-return valve is
defective; problem solved?
no
b
a b
Further pumps which are
connected to the solar tank
must also be checked.
Check the non-return valve in warm water cir-
culation - o.k.
yes
Clean or replace it.
The gravitation circulation
in the circulation line is too
strong; insert a stronger
valve in the non-return valve
or an electrical 2-port valve
behind the circulation pump;
the 2-port valve is open
when the pump is acti-
vated, otherwise it is closed;
connect pump and 2-port
valve electrically in parallel;
activate the circulation again.
Deactivate pump speed
control!
no
67