MF47-3.05
15
6.0
F
AULT
A
NALYSIS
A.
Furnace Does Not Heat Up
1.
The
HEAT
light
is
ON
An ohm meter applied to
the element circuit shows
an open circuit
A heating element has failed
2.
The
HEAT
light
is
OFF
The controller shows
a
very high temperature
or a code such as S.br
The thermocouple has broken
or has a wiring fault
The controller shows a
low temperature
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 fault light on the
control panel is on
The thermal cutout on the case
or in the transformer has
activated
There are no lights
glowing on the controller
Check the supply fuses and any
fuses in the furnace control
compartment
The controller may be faulty or
not receiving a supply due to a
faulty switch or a wiring fault
B.
Furnace Overheats
1.
The
HEAT
light
goes
OFF
with the
instrument switch
The controller shows a
very high temperature
The controller is faulty
The controller shows a
low temperature
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
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
The power thyristor has
failed “ON”
Check for an accidental wiring
fault which could have
overloaded the thyristor.
Isolate the furnace if this fault
persists.
