Viessmann VITODENS 100-W Installation And Service Instructions Manual page 40

Troubleshooting
Repairs
(cont.)
20
10
8
6
4
2
1
0.8
0.6
0.4
10 30 50 70 90 110
Temperature in °C
Checking volumetric flow rate
The volumetric flow rate through the
boiler is monitored by recording the dif-
ferential between boiler water tempera-
ture and return temperature. Monitoring
of the temperature spread with the boiler
water temperature sensor and the return
temperature sensor is an additional
safety mechanism.
40
2. Check the sensor resistance and
compare it with 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 temperature
sensor is immersed in the
heating water (risk of scald-
ing).
Drain the boiler before replac-
ing the sensor.
■ In the case of differentials
> 25 K/< 30 K, the burner is operated
at lower heating output.
■ In the case of differentials > 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 sufficient
heating water.