Viessmann Vitodens 100-W Installation And Service Instructions Manual page 45

Repairs
(cont.)
20
10
8
6
4
2
1
0.8
0.6
0.4
10 30 50 70 90 110
Temperature in °C
Flow rate monitoring
Flow switch
The boiler is equipped with a flow
switch for monitoring the minimum flow
rate.
The burner is shut down at a heating
water flow rate below 200 l/h. No fault
message is shown.
Recording the differential between
the boiler water temperature and
return temperature
The flow rate through the boiler is moni-
tored by recording the differential
between the boiler water temperature
and the return temperature. Monitoring
of the temperature spread with the
boiler water temperature sensor and
the return temperature sensor is an
additional safety mechanism.
2. Check sensor resistance and com-
pare it to the curve.
3. In the case of severe deviation,
drain the boiler on the heating
water side and replace the sensor.
Danger
The boiler water tempera-
ture sensor is directly
immersed in the heating
water (risk of scalding).
Drain the boiler before
replacing the sensor.
■ At a differential of > 25 K/< 30 K, the
burner is operated at the lower heat-
ing output.
■ At a differential of > 30 K, the burner
is switched off.
In such cases, check whether the heat-
ing system is adequately vented and
the circulation pump is pumping suffi-
cient heating water.
Troubleshooting
45