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TROUBLESHOOTING
Standing Pilot Models
Main Burner Does Not Ignite
1. Check the electrical supply to the furnace.
2. Verify the furnace furnace On-Off switch is in
the ON position.
3. Check for proper thermostat operation.
4. Check for broken or open thermostat wires.
5. Verify the insulation located on the inside of
the front panel is glued securely around the
fan switch and the limit switch.
6. Shut off the electrical supply to the furnace
and remove the electrical box cover.
7. Check for a defective transformer or blown
fuse.
8. Check electrical circuit for proper grounding,
polarity, and make sure the electrical
connections are tight.
9. Check the limit switches. Did they fail to close?
10. Replace the electrical box cover and restore
electrical power to the furnace. Turn the
furnace On-Off switch to ON and raise the
thermostat setting above room temperature.
11. Check for 24 VAC at the gas valve. Replace
the valve if the pilot is established and it
does not open when powered with 24 volts.
Powered (24 VAC) Gas Valve - No Main Flame
1. Verify the manual shut-off valve is OFF.
2. Check the pilot fl ame. It must be established.
3. Check the gas valve control lever. It must be
in the ON position.
4. Check incoming gas pressure.
5. Replace the gas valve if the main burner does
not come on under the above conditions.
Pilot Will Not Light or Goes Out
1. Check the incoming gas pressure.
2. Check for the proper pilot orifice. See
specifi cations on the furnace nameplate.
3. Check for proper pilot fl ame adjustment. See
Burner Adjustment section (page 22).
4. Verify the thermocouple millivoltage. If reading
is not between 18 - 30 mv., the gas valve
electromagnet may be defective. Replace the
gas valve if necessary.
5. Verify the pilot shield is in place.
6. Check for gas leaks (page 18).
7. Check the fl ue assembly for air leaks.
8. See lighting procedures (pages 20 - 22).
Main Flame Is Not Burning Properly
1. Check the manifold gas pressure.
2. Check for the correct main burner orifi ce. See
furnace nameplate for specifi cations.
3. Check the fl ue for any blockages or loose
connections.
4. Check the combustion air passages for
blockage.
High Gas Bills
a. Verify the proper orifi ces are being used.
b. Check the return air system. Is it clear and
free of blockage?
c. Check the furnace fi lter. Is it clean or need
replacing?
d. Verify the home is insulated, windows and
doors fi t tightly, and there are no leaks in the
heating duct system.
e. Check the room thermostat. Is the setting
higher than necessary? Low humidity requires
higher temperatures for the same level of
comfort. Check for proper humidity level in the
home.
Direct Ignition Furnaces Including Gas Gun
M1B Series (see Table 9, page 29)
Burner Motor won’t Run - T-stat Calls for Heat
1. Check the electrical supply to the furnace.
2. Verify the furnace furnace On-Off switch is in
the ON position.
3. Defective thermostat circuit - white and red
thermostat low voltage leads (M1/M5M,
M1/M5B models). If the burner motor or
combustion fan runs, check:
• Thermostat connections
• Thermostat
4. No voltage to control module - determine if 24
volts (or 120 volts) is available to the control
module. If voltage is not available check for:
• Blown fuse, defective transformer, circuit
breaker, no electrical supply.
• Limit switch open.
• Loose connections.
Combustion Blower Runs - No Flame
1. Defective centrifugal switch (M1B Model).
• Check the operation of centrifugal switch
by removing end bell of the burner motor.
• Clean contacts of motor.
• If the contacts are closed, replace the motor.
2. Defective pressure switch (M1M & M1G - 077,
090 Models) - check air tube and electrical
connections.
3. Burner in purge mode - allow 75 seconds for
fl ame establishing period.
4. Check for proper electrical connections at
purge timer, control box, or gas valve.
5. Check for gas supply - gas line valve on, control
lever on.
Control Module is Powered - Ignitor won’t Heat
Up
1. Disconnect ignitor leads at AMP receptacle and
check for 120 volts at the plug during ignition
sequence.
2. Replace ignition control if 120 volts is not
available at AMP plug during ignition sequence.