Cleaning The Ignition Electrode; Inspection, Replacement And Features Of Supply, Return And Flue Ntc Temperature Sensors - Bosch SSB85 Service Manual

28 | Maintenance schedule & procedures
8 .6

Cleaning the Ignition Electrode

The ignition electrode requires annual maintenance to remove any
potential oxide layer that may be generate during normal operation.
Check the high voltage cable for cracks and oxidation on the plug.
[1] Remove the ignition cable plug and check for oxidation;
Ignition plug
Fig. 78 Inition plug
In case of oxidation replace the entire cable;
[2] Remove the two fasteners retaining the electrode and extract the
electrode from the heat exchanger;
Fig. 79 Electrode fasteners
[3] Examine the electrode, if oxidation is found remove it with fine
sandpaper;
[4] Check the electrode spacing
Note: The distance must be between 3 and 5 mm;
[5] Re-insert the electrode with a new seal.
Fig. 80 Electrode
6720866940 (2017/11) US
fastners
electrode
electrode spacing: 3 to 5mm
8 .7 Inspection, replacement and features of supply,
return and flue NTC temperature sensors
The NTC sensor transduces a temperature value into an electrical
resistance. The characteristics of NTC sensor are reported on Tab. 12
below.
The supply, return and flue temperature sensors are immersion type and
have the same electrical characteristic (= 10 kΩ at 25°C).
To remove and replace the NTC probes turn off the boiler and follow the
procedure below:
[1] Disconnect the electrical plug from the sensor;
[2] Drain the water from the boiler before removing the water
temperature sensor. To verify proper functionality use an Ohm meter
to measure the resistance across the terminals with reference to
Table 12.
If the resistance is low the NTC sensor is in short circuit, while if the
resistance is very high the sensor is open. In both cases the sensor must
be replaced.
Supply temperature sensor
Fig. 81 Supply temperature sensor
Return temperature sensor
Fig. 82 Return temperature sensor
Flue temperature sensor
Fig. 83 Flue temperature sensor
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