Lennox G24M SERIES Unit Information page 35

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
Condition
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.
LED#1--On
LED#2--Slow Flash
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-
guard flame failure. guard flame failure.
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
PREMATURELY (CONT.)
Possible Cause
6.3.1
Unit is firing above 100% of the
nameplate input.
6.3.2
Gas orifices leak at the manifold
connection.
6.3.3
Insufficient flow through the heat
exchanger caused by a sooted or
restricted heat exchanger.
6.3.4
Burners are not properly located in
the burner box.
6.4.1
Recirculation of flue gases. This
condition causes rough ignitions
and operation. Problem is charac-
terized by nuisance flame failures.
6.4.2
Improper burner cross--overs
3DJH 
Corrective Action/Comments
Check that the manifold pressure
ACTION 1 - -
matches value listed on nameplate. See
installation instructions for proper proce-
dure.
Verify that the installed orifice
ACTION 2 - - size match the size listed on the nameplate or
installation instructions.
Check gas valve sensing hose to
insure no leaks are present. ACTION 3 - -
Check the input rate to verify rate
ACTION 4 - - matches value listed on nameplate.
Tightenorifice untilleakissealed.
ACTION 1 - - Be careful not to strip orifice threads.
NOTE: Check for gas leakage at the
ACTION 2 - - threaded orifice connection. Use approved
method for leak detection (see unit instruc-
tions).
Checkforsootingdepositsoroth-
ACTION 1 - -
er restrictions in the heat exchanger assem-
bly. Clean assemblyas outlined in instruction
manual.
For G24M gas furnaces, check for
ACTION 2 - -
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.
Check that the burners are firing
into the center of the heat exchanger open- ACTION 1 - -
ings. Correct the location of the burners if
necessary.
Check for proper flow of exhaust
gases away from intake vent. Remove any ACTION 1 - -
obstacles in front of the intake and exhaust
vent which would cause recirculation.
Check for correct intake and ex-
ACTION 2 - - haust vent installation. See instructions
Remove burner and inspect the
cross- - overs for burrs, or any restriction or if ACTION 1 - -
crossover is warped. Remove restriction or
replace burners.