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PROBLEM 5: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition
Possible Cause
Corrective Action/Comments
5.3
− Combustion air inducer energizes
with a heating demand.
− Burners light.
− Roll−out switch trips during the
heating demand.
− Diagnostic lights flash roll−out fail
ure.
5.3.1
Unit is firing above 100% of the
nameplate input.
ACTION 1 −
Check that the manifold pressure
matches value listed on nameplate. See installa
tion instructions for proper procedure.
ACTION 2 −
Verify that the installed orifice size
match the size listed on the nameplate or installa
tion instructions.
ACTION 3 −
Check gas valve sensing hose to in
sure no leaks are present.
ACTION 4 −
Check the input rate to verify rate
matches value listed on nameplate.
ure.
LED#1−On
LED#2−Slow Flash
5.3.2
Gas orifices leak at the manifold con
nection.
ACTION 1 −
Tighten orifice until leak is sealed.
NOTE:
Be careful not to strip orifice threads.
AC
TION 2 −
Check for gas leakage at the threaded
orifice connection. Use approved method for leak
detection (see unit instructions).
5.3.3
Air leakage at the connections be
tween the primary heat exchanger,
secondary heat exchanger, and com
bustion air blower.
ACTION 1 −
Check for air leakage at all joints in
the heat exchanger assembly. Condition will
cause high CO2 with high CO.
ACTION 2 −
Seal leakage if possible, replace
heat exchanger if necessary, tag and return heat
exchanger to proper Lennox personnel.
5.3.4
Insufficient flow through the heat ex
changer caused by a sooted or re
stricted heat exchanger.
ACTION 1 −
Check for sooting deposits or other
restrictions in the heat exchanger assembly.
Clean assembly as outlined in instruction manu
al.
ACTION 2 −
Check for proper combustion.
5.3.5
Burners are not properly located in
the burner box.
ACTION 1 −
Check that the burners are firing into
the center of the heat exchanger openings. Cor
rect the location of the burners if necessary.
5.4
−
Combustion air inducer energizes
with a heating demand.
− Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard
flame failure.
5.4.1
Recirculation of flue gases. This con
dition causes rough ignitions and op
eration. Problem is characterized by
nuisance flame failures.
ACTION 1 −
Check for proper flow of exhaust
gases away from intake vent. Remove any ob
stacles in front of the intake and exhaust vent
which would cause recirculation.
ACTION 2 −
Check for correct intake and exhaust
vent installation. See instructions
flame failure.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
5.4.2
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 re
place burners.