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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 inducer energizes
with a heating demand.
− Burners light.
− Roll−out switch trips during the
heating demand.
Diagnostic lights flash roll out fail
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 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.
− Diagnostic lights flash roll−out fail-
ure.
LED#1−On
6.3.2
Gas orifices leak at the manifold con-
nection.
ACTION 1 −
Tighten orifice until leak is sealed.
NOTE:
Be careful not to strip orifice threads.
ACTION 2 −
Check for gas leakage at the
threaded orifice connection. Use approved
method for leak detection (see unit instructions).
LED#1 On
LED#2−Slow Flash
6.3.3
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.
See IV−Heating System Service Checks
section NO TAG.
6.3.4
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.
6.4
−
Combustion air inducer energizes
with a heating demand.
− Burners light roughly and the unit
6.4.1
Poor Venting
ACTION 1
−Check vent pipe and remove any ob-
structions
ACTION 2 −
Check for correct exhaust vent
installation. See instructions
Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard
flame failure.
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 re-
place burners.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
6.4.3
Burrs in gas orifices
ACTION 1 −
Remove gas orifices and inspect.
Remove any burrs that are present or replace ori-
fice.
