Lennox G40UH(X)

Page 45
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
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 the input rate to verify rate
matches value listed on nameplate.
− Diagnostic lights flash roll−out fail-
ure.
LED#1−On
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.
ACTION 2 − Check for gas leakage at the
threaded orifice connection. Use approved meth-
od for leak detection (see unit instructions).
LED#1 On
LED#2−Slow Flash
5.3.3
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.
5.3.4
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.
5.4
− Combustion air inducer energizes
with a heating demand.
B li ht hl d th it
5.4.1
Poor Venting
ACTION 1 −Check vent pipe and remove any ob-
structions
ACTION 2 − Check for correct exhaust vent
installation. See instructions
g
− Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard
flame failure.
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.
flame
failure
.
LED#1−Alternatin
g
Slow Flash
5.4.3
Burrs in gas orifices
ACTION 1 − Remove gas orifices and inspect.
Remove any burrs that are present or replace ori-
fice.
LED#1−Alternating
Slow
Flash
LED#2−Alternating Slow Flash
5.4.4
Prove Switch opens 5 times during a
single demand
ACTION 1 − Inspect vent pipe installation and for
any restriction. Remove restriction.
ACTION 2 − Check prove switch reliability.
5.5
− Combustion air inducer energizes
with a heating demand.
− Burners light.
− Diagnostic lights flash watch guard
flame failure.
− NOTE" Unit might go into 60 minute
Wth d d d di i
5.5.1
Loose sensor wire connection causes
intermittent loss of flame signal.
ACTION 1 − Check that the sensor is properly lo-
cated.
ACTION 2 − Check that the sense wire is properly
attached to both the sensor and the control. Pay
extra attention to the pin connectors.
gg
Watchguard mode depending on in-
termittent nature of sensor signal.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
5.5.2
Poor ground to burner box
ACTION 1 − Check for proper ground and repair
as necessary.