– Measure the voltage to the bypass valve V4 (28)
24 Volts DC while the furnace is open is normal.
Zero volts when the furnace is closed is normal.
– Clean the valves
3.4.2 Resistance furnace operation
No combustion:
The operating temperature is mostly 1350°C so that it is easy to recognize by looking into the
furnace, whether the furnace is hot or not.
Caution For looking into the furnace be sure to wear protective glasses and to hold radiation
absorbing glass in front of your eyes.
In case the furnace is hot but still there are doubts about the true of the temperature, the
resistance furnace temperature can be measured by entering a thermocouple connected to
appropriate digital thermometer.
: Temperature control
The tip of the thermocouple should be in the middle of the hot zone where the combustion boat
use to be. The thermocouple must be long enough in order to make sure that the junction of the
thermocouple wires to the cable does not become hot. A thermocouple length of 50 cm is
appropriate. In case the furnace temperature is over 1000°C the thermocouple has to be of type
S. It is not usual to have it in this length available. If a 300mm type S thermocouple is available,
a compromise is to enter the tip up to the beginning of the hot zone to prevent the junction
temperature of the cable from overheating. If this is not available then set the furnace
temperature to 1000°C and check with a long type K or N thermocouple.
In case the resistance furnace is completely cold:
- check the set temperature. If there is nothing shown on the display, then check the
availability of mains power. Take a look at the breaker on the back of the furnace and at
the breaker of the power line.
- If the display shows the right “Set point” and the displayed actual “Furnace temperature”
is displayed very low but corresponding to the real furnace temperature, most probably
the heating elements are worn out and broken so that they have to be replaced. See
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