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PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition Possible Cause Corrective Action/Comments
6.3
- Combustion air blower energizes
with a heating demand.
- Burners light.
- Roll-out switch trips during the
heating demand.
- Diagnostic lights flash roll-out failĆ
ure.
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 installaĆ
tion instructions for proper procedure.
ACTION 2 - Verify that the installed orifice size
match the size listed on the nameplate or instalĆ
lation instructions.
ACTION 3 - Check gas valve sensing hose to inĆ
sure 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 conĆ
nection.
ACTION 1 - Tighten orifice until leak is sealed.
NOTE: Be careful not to strip orifice threads. ACĆ
TION 2 - Check for gas leakage at the threaded
orifice connection. Use approved method for
leak detection (see unit instructions).
6.3.3
Air leakage at the connections beĆ
tween the primary heat exchanger,
secondary heat exchanger, and comĆ
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 (high temĆ
perature silicon is recommended), replace heat
exchanger if necessary, tag and return heat exĆ
changer to proper Lennox personnel.
6.3.4
Insufficient flow through the heat exĆ
changer caused by a sooted or reĆ
stricted heat exchanger.
ACTION 1 - Check for sooting deposits or other
restrictions in the heat exchanger assembly.
Clean assembly as outlined in instruction manuĆ
al.
ACTION 2 - For G26 gas furnaces, check for
proper combustion and flow. CO2 should meaĆ
sure between 6.0% and 8.0% for NG and beĆ
tween 7.5% and 9.5% for LP. CO should meaĆ
sure below .04% (400PPM) in an air-free sample
of flue gases for either NG or LP.
6.3.5
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. CorĆ
rect the location of the burners if necessary.
6.4
- Combustion air blower energizes
with a heating demand.
- Burners light roughly and the unit
fails to stay lit.
- Diagnostic lights flash watchguard
flame failure.
6.4.1
Recirculation of flue gases. This conĆ
dition causes rough ignitions and opĆ
eration. Problem is characterized by
nuisance flame failures.
ACTION 1 - Check for proper flow of exhaust
gases away from intake vent. Remove any obĆ
stacles in front of the intake and exhaust vent
which would cause recirculation.
ACTION 2 - Check for correct intake and exĆ
haust vent installation. See instructions
.
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 reĆ
place burners.
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