Lennox G50UHi Unit Information page 32

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
Condition
6.3
− Combustion air inducer energizes
with a heating demand.
− Burners light.
− Roll−out switch trips during the
heating demand.
− Diagnostic lights flash roll−out fail- Diagnostic lights flash roll out fail
ure.
LED#1 On LED#1−On
LED#2−Slow Flash
6.4
− Combustion air inducer energizes
with a heating demand.
− Burners light roughly and the unit Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard
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
Poor Venting
6.4.2
Improper burner cross−overs
6.4.3
Burrs in gas orifices
Page 32
Corrective Action/Comments
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 the input rate to verify rate
matches value listed on nameplate.
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 sooting deposits or other
restrictions in the heat exchanger assembly.
Clean assembly as outlined in instruction manu-
al.
ACTION 2 − Check for proper combustion.
See IV−Heating System Service Checks
section G−.
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 vent pipe and remove any ob-
structions
ACTION 2 − Check for correct 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 − Remove gas orifices and inspect.
Remove any burrs that are present or replace ori-
fice.