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VZ-VZH-VZT-IOM (08-24) 1047121-A
Table 18. General Troubleshooting
Symptom Probable Cause Remedy
A. With
thermostat
turned up,
blower does
not turn ON
1. Obstructed blower Remove blower obstruction
2. No 120V at burner Ensure that 120V is available at burner
3. Faulty relay wiring or wiring to burner Ensure that relay wiring and wiring to burner are sound
4. Faulty thermostat wiring Ensure that thermostat wiring is sound
5. Faulty thermostat Replace thermostat
6. Failed blower motor bearings or faulty motor Replace blower motor
B. No spark
at ignitor
1. Obstructed vent pipe Remove vent pipe obstruction
2. Obstructed combustion air inlet Remove combustion air inlet obstruction
3. Incorrect spark gap Ensure that spark gap is 1/8 inch (3.2 mm)
4. Loose or damaged pressure switch tubing Tighten, repair, or replace pressure switch tubing
5. Faulty ignitor wiring Ensure that ignitor wiring is sound
6. Faulty ignitor Replace ignitor
7. Faulty wiring between blower motor and transformer Remove blue and yellow wires from transformer:
• If there is no 24V at transformer secondary and no 120V at black
and white transformer leads, ensure that wiring between blower
motor and transformer is sound—if 120V is present at black and
white transformer leads, replace transformer
• If 24V is present at transformer secondary, reconnect blue
and yellow transformer wires and connect jumper wire across
pressure switch—if there is spark, replace pressure switch—if
there is no spark replace ignition control module
8. Faulty transformer
9. Faulty pressure switch
10. Faulty ignition control module
C. Burner
does not light
1. Air in gas line Purge air from gas line
2. Combination gas valve set to OFF Ensure that combination gas valve is set to ON
3. Incorrect gas supply pressure Ensure that supply pressure is in accordance with Gas Supply
Pressure section
4. Incorrect manifold gas (outlet) pressure Ensure that pressure is in accordance with Measure and Adjust
Manifold Gas (Outlet) Pressure section
5. Loose wiring connection Ensure that all wiring connections are sound
6. No spark Ensure that spark gap is 1/8 inch (3.2 mm)
Check transformer—replace as necessary
Check ignition control module—replace as necessary
D. Burner
lights but
does not
remain ON
1. Dirty or damaged electrode Clean or replace electrode as necessary
2. Loose wiring connection or incorrect polarity Ensure that all wiring connections are sound
3. Faulty ignition control module Check ignition control module—replace as necessary
E. Burner
does not turn
OFF when
call for heat
ends
1. Faulty ground wire Ensure continuity of ground wire
2. Faulty thermostat Replace thermostat
F. Model VZT
burner status
indicator
light(s) not
functioning
properly
1. Faulty bulb Replace bulb
2. Faulty thermostat wiring Ensure that thermostat wiring is sound
3. Faulty thermostat Replace thermostat
4. Faulty combination gas valve Check combination gas valve—replace as necessary
5. Faulty ignition control module Check ignition control module—replace as necessary
TROUBLESHOOTING
General Troubleshooting
Troubleshooting Using Ignition Control Module
Table 19. Troubleshooting Using Ignition Control Module
LED Status Indication
Steady ON Internal control failure—replace module
Two flashes Flame without call for heat
Three flashes Lockout from three ignition trials
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