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BLF
F
A
AULT
NALYSIS
A. Furnace Does Not Heat Up
1.
The HEAT light
is ON
2.
The HEAT light
is OFF
B. Furnace Overheats
1.
The HEAT light
goes OFF with the
instrument switch
2.
The HEAT light
does not go off with
the instrument
switch and the fault
persists when a 2A
control fuse is
removed from its
fuse-holder
7.0
12
An ohm meter applied to
the element circuit shows
an open circuit
The controller shows a
very high temperature
or a code such as S.br
The controller shows a
low temperature
There are no
lights glowing
on the
controller
The controller shows a
very high temperature
The controller shows a
low temperature
The power thyristor has
failed "ON"
A heating element has failed
The thermocouple has broken
or has a wiring fault
The door switch may be faulty
or need adjustment
The thyristor fuse may have
blown
The power thyristor could be
failing to switch on due to
internal failure, faulty wiring
from the controller, or faulty
controller
The SUPPLY light is
ON
The SUPPLY light is
OFF
The controller is faulty
The thermocouple may have
been shorted out or may have
been moved out of the furnace
The thermocouple may be
mounted the wrong way round
The controller may be faulty
Check for an accidental wiring
fault which could have
overloaded the thyristor.
Isolate the furnace if this fault
persists.
The controller may
be faulty or not
receiving a supply
due to a faulty switch
or a wiring fault
Check the supply
fuses and any fuses in
the furnace control
compartment
MF23
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