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PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)
Condition Possible Cause Corrective Action/Comments
5.1
– Unit operates with a cooling and
continuous fan demand.
Combustion air blower energizes
5.1.1
Check that gas is being supplied to
the unit.
ACTION 1 – Check line pressure at the gas
valve. Pressure should not exceed 13” WC for
both natural and propane. Line pressure
should read a minimum 4.5” WC for natural
and 8.0”WC for propane.
–
with Heating demand.
– Ignitor is energized but unit fails
to light.
5.1.2
Miswiring of gas valve or loose
connections at multi–pin control
amp plugs or valve.
ACTION 1 – Check for correct wiring and loose
connections. Correct wiring and/or replace
any loose connections.
LED#1–Alternating Slow Flash
LED#2–Alternating Slow Flash
5.1.3
Defective gas valve or ignition con-
trol.
ACTION 1 – Check that 24V is supplied to the
gas valve approximately 35 seconds after heat
demand is initiated.
ACTION 2 – Replace the valve if 24V is sup-
plied but valve does not open.
ACTION 3 – Replace the control board if 24V is
not supplied to valve.
PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY
Condition Possible Cause Corrective Action/Comments
6.1
– Burners fire with a heating de-
mand.
6.1.1
Wrong concentric vent kit used for
terminating the unit.
ACTION 1 – Check vent termination kit
installed. 1–1/2” dia. concentric vent
(kit60G77) for 50 and 75 inputs and 2” dia. con-
centric vent (kit 33K97) for 100 &125 inputs.
– Burners light but unit shuts off
prior to satisfying T–stat demand.
– Diagnostic lights flash the pres-
sure switch code.
6.1.2
Condensate drain line is not drain-
ing properly.
ACTION 1 – Check condensate line for proper
vent slope, and any blockage. Condensate
should flow freely during operation of fur-
nace. Repair or replace any improperly
installed condensate lines.
LED#1–Off
LED#2–Slow Flash
6.1.3
Low pressure differential at the
pressure switch.
ACTION 1 – Check for restricted vent inlet or
exhaust. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
6.2
– Combustion air blower energizes
with a heating demand.
B ne s li ht b t fail to sta lit
6.2.1
Sensor or sense wire is improperly
installed.
ACTION 1 – Check that sensor is properly
located and that the sense wire is properly
attached to both the sensor and the control.
–
urners
g
u
a
o s
ay
.
– After 5 tries the control diagnostics
flash the watchguard burners failed
to ignite code.
6.2.2
Sensor or sense wire is broken.
ACTION 1 – Check for a broken sensor.
ACTION 2 – Test continuity across the sense
wire. If wire or sensor are damaged replace
the component.
LED#1–Alternating Slow Flash
LED#2–Alternating Slow Flash
6.2.3
Sensor or sensor wire is grounded
to the unit.
ACTION 1 – Check for resistance between
the sensor rod and the unit ground.
ACTION 2 – Check for resistance between
the sensor wire and the unit ground.
ACTION 3 – Correct any shorts found in cir-
cuit.
6.2.4
Control does not sense flame.
ACTION 1 – Check the microamp signal from
the burner flame. If the microamp signal is
below 0.70 microamps, check the sense rod
for proper location or contamination.
ACTION 2 – Replace, clean, or relocate flame
sense rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN
ROD WITH SAND PAPER. SAND PAPER
WILL CONTRIBUTE TO THE CONTAMI-
NATION PROBLEM. NOTE: Do not attempt
to bend sense rod.
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