Full Product Manual

Troubleshooting Your Furnace
38
SYMPTOM
POSSIBLE CAUSE(S)
CORRECTIVE ACTION
1. Pilot will not stay
lit after following
lighting
instructions.
a. Generator producing
insufficient millivolts.
b. Loose or dirty generator
connections at gas valve.
c. Generator defective.
d. Grounded thermostat wire.
e. Defective gas valve.
a. Check pilot flame. It must impinge on the generator.
b. Clean and/or tighten generator connections at valve.
c. Check generator with millivolt meter. Take reading at generator
terminals of the valve with the valve placed in “Pilot” position.
Disconnect the thermostat wires. The millivolt reading should be
450 millivolts or more.
d. Remove thermostat wires from valve terminals. If pilot now stays lit,
trace thermostat wiring circuit for a ground. May be grounded to
furnace, gas supply, nails or staples.
e. Replace gas valve after above is verified.
2. No gas to the
main burner.
a. Gas valve not turned to the
“ON” position after lighting
pilot.
b. Thermostat not tuned to a
position calling for heat.
c. Plugged furnace orifice.
d. Improper wired or broken
thermostat wires. Defective
thermostat.
e. Pilot generator may not be
generating sufficient
millivolts to open valve.
f. Defective valve.
g. Vent safety switch tripped.
a. Turn gas valve knob to the “ON.”
b. Set thermostat to a position calling for heat.
c. Checkclean or replace.
d. Check connections at valve terminals. If valve operates, check
thermostat wires.
e. See 1a and 1c above.
f. Replace gas valve after above is verified.
g. Check and reset.
3. Furnace
operates but
turns off before
room
temperature is
attained.
a. Thermostat location.
b. Defective thermostat.
a. Check thermostat location. It should not be in the path of warm air
discharge from furnace, near a lamp or above a T.V. or stereo unit.
b. Check thermostat calibration or replace.
4. Furnace not
producing
sufficient heat.
a. Furnace may be too small for
space being heated.
b. Furnace not burning at full
rate.
a. Check heat sizing calculations.
b. Check for low gas pressure at gas valve. It should be 4 inches
water column for natural gas; 10-inches water column for L.P.G.
Check for blocked burner orifices.
5. Furnace
operates but will
not shut off
when room
temperature is
attained.
a. Thermostat wiring defective.
b. Thermostat location.
c. Defective thermostat.
d. Valve stuck open.
a. Thermostat lead wires may be shorted together, caused by a nail or
staple. Check by removing thermostat leads from valve terminals.
b. Check thermostat location. If on an outside wall, or there is a hole
in the wall behind the thermostat, cold air may be coming in contact
with the thermostat. Relocate.
c. Check thermostat calibration; verify thermostat temperature
reading; or replace.
d. Replace valve.