Table of Contents
Advertisement
14 Fault analysis
A.
Furnace does not heat up
1.
The HEAT light
is ON
2.
The HEAT light
is OFF
3.
Fuse blows or
earth leakage
device trips as
soon as furnace
starts to heat.
MF 55-GB 1.21
The element circuit has
failed
The controller shows a
very high temperature
and code S.br
The controller shows a
low temperature
The fault light on the
control panel is on
There
The
are no
SUPPLY
lights
light is ON
glowing
on the
The
controller
SUPPLY
light is
OFF
Element insulating mica
washer has failed.
Check 1: A visual inspection of the
elements inside the chamber for
signs of failure
Check 2: Isolate the MRF 16/22 from
the electrical supply; disconnect the
element circuit from the transformer
secondary windings, check the
continuity of the element circuit.
Open circuit indicates element
failure.
The thermocouple has failed and
gone open circuit
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 thermal cutout on the case or in
the transformer has activated
The controller may be faulty or not
receiving a supply due to a blown
instrument circuit fuse, faulty switch
or a wiring fault
Check the supply fuses and any
fuses in the furnace control
compartment
Check: Isolate the MRF 16/22 from
the electrical supply; remove the top
access panel and element tails MW
shield lid. Disconnect element circuit
form transformer secondary
windings. Check resistance between
element tails and brickbox case. If
this is low (below 500k then
remove element braids and check
each element tail until the one
causing the low resistance is
identified. Replace mica washer
(refer to section 13.9 for mica
washer replacement) and recheck
resistance.
MRF 16/22
49
Advertisement
Table of Contents
