Lennox G24M SERIES

3DJH  
PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition Possible Cause Corrective Action/Comments
6.3
-- Combustion air blower ener-
gizes with a heating demand.
-- Burners light.
-- Roll--out switch trips during the
heating demand.
-- Diagnostic lights flash roll--out
failure.
6.3.1
Unit is firing above 100% of the
nameplate input.
ACTION 1 --
Check that the manifold pressure
matches value listed on nameplate. See
installation instructions for proper proce-
dure.
ACTION 2 --
Verify that the installed orifice
size match the size listed on the nameplate or
installation instructions.
ACTION 3 --
Check gas valve sensing hose to
insure no leaks are present.
ACTION 4 --
Check the input rate to verify rate
matches value listed on nameplate.
LED#1--On
LED#2--Slow Flash
6.3.2
Gas orifices leak at the manifold
connection.
ACTION 1 --
Tighten orifice until leak is sealed.
NOTE:
Be careful not to strip orifice threads.
ACTION 2 --
Check for gas leakage at the
threaded orifice connection. Use approved
method for leak detection (see unit instruc-
tions).
6.3.3
Insufficient flow through the heat
exchanger caused by a sooted or
restricted heat exchanger.
ACTION 1 --
Checkfor sooting deposits or oth-
er restrictions in the heat exchanger assem-
bly. Clean assembly as outlined in instruction
manual.
ACTION 2 --
For G24M gas furnaces, check for
proper combustion and flow. CO2 should
measure between 6.0% and 8.0% for NG and
between 6.5% and 8.5% for LP. CO should
measure below .04% (400PPM) in an air--free
sample of flue gases for either NG or LP.
6.3.4
Burners are not properly located in
the burner box.
ACTION 1 --
Check that the burners are firing
into the center of the heat exchanger open-
ings. Correct the location of the burners if
necessary.
6.4
-- Combustion air blower ener-
gizes with a heating demand.
-- Burners light roughly and the
unit fails to stay lit.
-- Diagnostic lights flash watch-
g
uard flame failure.
6.4.1
Recirculation of flue gases. This
condition causes rough ignitions
and operation. Problem is charac-
terized by nuisance flame failures.
ACTION 1 --
Check for proper flow of exhaust
gases away from intake vent. Remove any
obstacles in front of the intake and exhaust
vent which would cause recirculation.
ACTION 2 --
Check for correct intake and ex-
haust vent installation. See instructions
guard flame failure
.
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
6.4.2
Improper burner cross--overs
ACTION 1 --
Remove burner and inspect the
cross--overs for burrs, or any restriction or if
crossover is warped. Remove restriction or
replace burners.