20
d. Check the thermocouple millivoltage.
•
Millivoltage should read between 18 and 30 mv.
•
If the closed millivolt reading is not between 18 and 30
mv., the gas valve electromagnet may be defective.
Replace the gas valve if necessary.
e. Be sure the pilot shield is in place.
f. Check for gas leaks in the pilot line or the pilot assembly.
g. Check the flue assembly to make sure all connections are
tight.
h. See the FURNACE START-UP procedure for lighting
details.
Main Flame Is Not Burning Properly
a. Check the manifold gas pressure.
b. Check for the correct main burner orifice.
- See the nameplate SPECIFICATION.
c. Check the flue for any blockages or loose connections.
d. Check the combustion air passages for blockage.
High Gas Bills
a. Be sure the proper orifices are being used.
b. Be sure the return air system is clear and free of blockage.
c. Be sure the furnace filter is clean.
d. Be sure the home is insulated, that windows and doors fit
tightly, and that there are no leaks in the heating duct
system.
e. Check the room thermostat to be sure the setting is not
higher than necessary. Low humidity requires higher
temperatures for the same level of comfort. Check for
proper humidity level in the home.
TROUBLESHOOTING -
DIRECT IGNITION FURNACES INCLUDING GAS GUN
Burner Motor Does Not Run—
Thermostat Calls For Heat
a. Check the electrical supply to the furnace.
b. Be sure the furnace On-Off switch is in the “ON” position.
c. Defective thermostat circuit - white and red thermostat
low voltage leads (M1M*, M1B* models). If the burner
motor or combustion fan runs, check:
•
Thermostat connections
•
Thermostat
k. Open the manual shut-off valve and follow the FURNACE
START-UP procedure as outlined previously in this manual
to put the furnace into operation.
NOTE: The pilot flame is adjustable by turning the adjustment
screw located on the gas valve with a small screwdriver. (See
Figure 29)
TROUBLESHOOTING - STANDING PILOT MODELS
Main Burner Does Not Come On
a. Check the electrical supply to the furnace.
b. Be sure the furnace On-Off switch is in the “ON” position.
c. Check for proper thermostat operation.
d. Check for broken or open thermostat wires.
e. Check to make sure the insulation located on the inside
of the front panel is glued securely around the fan switch
and the limit switch.
f. Shut off the electrical supply to the furnace and remove
the electrical box cover.
g. Check for a defective transformer or blown fuse.
h. Check electrical circuit for proper grounding, polarity, and
make sure the electrical connections are tight.
i. Check to see if limit switches may have failed to close.
j. Replace the electrical box cover and restore electrical
power to the furnace. Turn the On-Off switch to “ON” and
raise the thermostat setting above room temperature.
k. Check for 24 volts at the gas valve.
l. Replace the gas valve if the pilot is established and it does
not open when powered with 24 volts.
Gas Valve Powered (24 volts)– No Main Flame
a. The manual shut-off valve must be on.
b. The pilot flame must be established.
c. The gas valve control lever must be in the “ON” position.
d. Check gas pressure coming to the gas valve.
e. Replace the gas valve if the main burner does not come
on under the above conditions.
Pilot Will Not Light or Goes Out
a. Check the incoming gas pressure.
b. Check for the proper pilot orifice. See the nameplate
SPECIFICATION.
c. Check for proper pilot flame adjustment. See “BURNER
ADJUSTMENTS.”
Figure 33. Convertible Pressure Regulator Cap
PRESSURE
REGULATOR
CAP
M11678
N
A
T N
A
T
L
P
L
P
N
A
T N
A
T
OR
OTHER SIDE
OF CAP
Figure 34. Convertible Pressure Regulator
Honeywell
Valve
Robertshaw
Valve
