Lennox G43UF SERIES Unit Information page 54

PROBLEM 5: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
Condition
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. ure.
LED#1−On
LED#2−Slow Flash
5.4
− Combustion air inducer energizes
with a heating demand.
− Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard Di ti li ht fl h
flame failure.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
PREMATURELY (CONT.)
Possible Cause
Unit is firing above 100% of the
nameplate input.
Gas orifices leak at the manifold con-
Air leakage at the connections be-
tween the primary heat exchanger,
secondary heat exchanger, and com-
bustion air blower.
Insufficient flow through the heat ex-
changer caused by a sooted or re-
stricted heat exchanger.
Burners are not properly located in
the burner box.
Recirculation of flue gases. This con-
dition causes rough ignitions and op-
eration. Problem is characterized by
nuisance flame failures.
t h d
Improper burner cross−overs
Prove Switch opens 5 times during a
single demand
tion instructions for proper procedure.
5.3.1 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.
5.3.2
nection.
5.3.3
5.3.4
5.3.5
5.4.1
5.4.2
5.4.3
Page 54
Corrective Action/Comments
ACTION 1 − Check that the manifold pressure
matches value listed on nameplate. See installa-
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 meth-
od for leak detection (see unit instructions).
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.
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.
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.
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
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.
ACTION 1 − Inspect vent pipe installation and for
any restriction. Remove restriction.
ACTION 2 − Check prove switch reliability.