Page. 20 of 29
March 2016
Edition 1
PLANAR
5.5. Functions, Removal and Replacement of Flame Indicator.
Flame indicator is used to monitor presence of flame in the combustion chamber. It is
a metal tube with a built-in thermocouple.
If an error is displayed when the heater is turned on, check the flame indicator for
continuity with a tester. If there is a break, the indicator is defective and should be
replaced;
Check the flame indicator channel of the control unit. For that, set a jumper instead of
the flame indicator (Figure 9). If the flame indicator fault code is not displayed at the start
of the heater, the CU is OK. Turn off the heater and remove the jumper.
Check insulation resistance between the terminals and the indicator casing. The
resistance should be not less than 100 MOhm at a voltage of 100V. Ambient temperature
during resistance measurements should be between 15 and 35°C, relative humidity less
than 80%. If insulation resistance does not corresponds to this requirement, it is necessary
to replace the flame indicator.
If an error occurs during operation of the heater, it is possible that there is a crack
(open circuit fault) in the junction of the thermocouple of the flame indicator. There are
two methods to identify the problem:
1. Turn out the flame indicator, connect its contacts to the multimeter (to the
terminals of temperature measurement) and heat the sensor, for instance with a cigarette
lighter. The observed temperature rise should be smooth. If the temperature changes
suddenly, or assumes its initial value, the indicator is damaged. In such a case, the open
circuit fault may disappear after cooling off of the indicator.
2. Turn out the flame indicator from the housing, and measure the voltage generated
by the indicator when heated. When the indicator casing is at+100°C (temperature of
boiling water), the voltage should be approximately 3millivolts. The voltage on the
terminal marked with a red tubing, should be of positive polarity with respect to the
terminal marked with a black tubing.
In the case of an open circuit fault, the flame indicator is defective and should be
replaced.
To avoid mistakes when evaluating performance of the flame indicator, it is
necessary to substitute it with a known-good. If the cause of the heater failure is
eliminated with the installation of a new flame indicator, then the old flame indicator is
considered to be inoperable and has to be replaced.
If the problem persists, check the polarity of the connection of the flame indicator to
the CU (wire with black marking is connected to the connector terminal of the CU with a
black dot, Fig. 7b). A magnet can be used to check the correctness of wire marking.
Contact of the wire with the black mark is magnetic.