Troubleshooting
Guide
17|
Page
4)
If
the
error
code
persists,
replace
the
thermistor.
ERROR
CODE
331:
MIXING
THERMISTOR
1)
Check
that
the
wire
connections
are
secure
and
free
of
burns
or
cuts.
The
mixing
thermistor
is
embedded
in
the
water
outlet
connection.
2)
Check
the
resistance
value;
it
should
be
about
9.0k
Ω
at
room
temperature
(about
74°F).
3)
Clean
the
thermistor.
a.
Drain
the
unit
of
water.
See
p.
23.
b.
Remove
the
computer
board
to
access
the
mixing
thermistor.
The
computer
is
fixed
in
place
by
a
single
screw
at
the
top
of
the
board.
c.
Remove
the
screw,
pull
out
the
sensor
probe.
Clean
the
probe
to
a
silver
finish.
Do
not
lose
the
red
rubber
o
‐
ring
that
wraps
around
this
sensor.
d.
Replace
and
test.
4)
If
the
error
code
persists,
replace
the
thermistor.
ERROR
CODE
341:
EXHAUST
THERMISTOR
1)
Check
that
the
wire
connections
are
secure
and
free
of
burns
or
cuts.
The
exhaust
thermistor
is
embedded
at
the
top
center
of
the
unit
above
the
heat
exchanger.
2)
Check
the
resistance
of
the
thermistor.
The
value
should
be
about
10.75k
Ω
at
room
temperature
(about
74°F).
3)
Clean
the
thermistor.
a.
Remove
the
screw
holding
the
thermistor
plate,
then
pull
out
the
sensor
probe.
b.
Clean
the
probe
to
a
silver
finish.
Do
not
lose
the
white
gasket
that
seals
this
sensor.
c.
Replace
and
test.
4)
If
the
error
code
persists,
replace
the
thermistor.
ERROR
CODE
391:
AIR
‐
FUEL
RATIO
ROD
FAILURE
1)
Check
that
the
wire
connections
are
secure
and
free
of
burns
or
cuts.
2)
Check
that
the
clear
plastic
tube
connecting
the
proportional
gas
valve
to
the
combustion
chamber
is
attached.
3)
Clean
the
AFR
(p.
27).
Figure
12
Figure
13
Figure
14