22
221691B
Closed Circuit Voltage (millivolts)
DIAGNOSIS GRAPH FOR
THERMOCOUPLE CIRCUIT
Open Circuit Voltage (millivolts)
0246810121416182022
9
11
13
15
17
19
21
23
25
27
29
ABC
Diagram 10.3
THERMOCOUPLE FAULT FINDING
10 Fault Finding - Thermocouple
Diagram 10.4
1546
Disconnect appliance thermocouple from the multi-functional control. Check that all connections
are clean and in good condition. Fit test meter interrupter into the magnet unit. Fit appliance
thermocouple into the test meter interrupter.
NO
YES
Hold down control tap in ignition position. Ignite burner, allowing thermocouple to attain
operating temperature. Measure the OPEN CIRCUIT voltage.
Is
voltage
greater
than
15mV?
Faulty thermocouple.
Replace.
Note the open circuit reading then measure the CLOSED CIRCUIT voltage. Note this voltage.
Referring to the diagnosis graph, mark the open circuit voltage on the VERTICAL axis,
and the closed circuit voltage on the HORIZONTAL axis. Note the point where these
two values intersect on the graph.
THERMOCOUPLE
CIRCUIT IS
SATISFACTORY
In
which
area of the
graph is the
intersect
Faulty thermocouple.
Replace.
Faulty magnet unit in multi-functional
control. Replace.
B
A
C
0194
10.2 Thermocouple
To test the thermocouple a meter with a range of 0 to 30mV is
required together with a thermocouple interrupter test unit
similar to the British Gas Minitest 6 Unit.
Refer to thermocouple fault finding chart, diagram 10.3 and
diagnosis graph, diagram 10.4.
10.3 Pilot
Refer to pilot fault finding chart, see diagram 10.5.
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