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TROUBLESHOOTING YOUR FURNACE
For qualified service technicians.
ISSUE
1. Pilot will not stay lit
after following lighting
instructions.
2. Main burner will not come
ON (pilot burning
and thermostat set
for heat).
3. Burner comes "ON" but
goes OFF before blower
turns ON.
4. Burner comes "ON", blower
comes "ON", but cycles
"ON" and "OFF" while
burner remains "ON".
5. Burner comes "ON",
blower comes "ON", but
burner cycles "OFF" and
"ON" with blower "ON".
34
COUNTERFLOW TOP VENT GAS WALL HEATER
POSSIBLE CAUSE(S)
A. Thermocouple producing
insufficient millivolts.
B. Loose or dirty thermocouple
connection at gas valve.
C. Thermocouple defective.
D. Thermomagnet pilot safety defective
E. Vent safety shutoff
A. Gas valve not turned ON after
lighting the pilot.
B. Electric power to furnace
turned OFF.
C. Low voltage transformer or
limit switch defective.
D. Wall thermostat defective.
E. Burner orifice plugged.
F. Gas valve defective.
A. Defective wiring.
B. Defective limit switch.
C. Defective motor (2 speed).
D. Defective motor ( 1 speed).
E. Detective fan switch.
A. Furnace not operating at
full rate.
A. Furnace operating over-rate.
B. Line voltage too low.
C. Recirculation.
CORRECTIVE ACTION
A. Check pilot flame – it must impinge on thermocouple. Pilot flame may
be low or blowing (high) causing safety to drop out. Pilot orifice
or aerating hole may be plugged (check for spiders, webs or other
organic material). Be sure the thermocouple is fully inserted in its bracket.
B. Clean and/or tighten the thermocouple fitting at the connection to
the valve.
C. Check thermocouple with millivolt meter – it should generate approximately
30 millivolts when not connected to a load. When connected to a load, it
should generate approximately 14 millivolts. If below 7 millivolts, replace.
D. Replace gas valve after above is checked out.
E. Check wiring connections from valve to the vent safety shutoff device. Be
sure all connections are tight. Check for blocked or incorrect venting.
A. Turn gas valve knob to 'ON" position (if no main gas flow, proceed to Step "B").
B. Check for line voltage at furnace (if okay and no main gas flow, proceed to
Step "C").
C. Check for 24 volts at the low voltage terminals of the transformer. If no
voltage, turn OFF electric power to furnace. Remove one wire from limit
switch and check for continuity across both terminals. No continuity –
replace limit switch. With a good limit switch back in the circuit and the
electric power turned ON (if no voltage, replace transformer. NOTE:
Before replacing the transformer or limit switch, check wiring for loose
connections or broken wires and repair as needed. If voltage is present at
transformer, proceed to Step "D").
D. With thermostat set for heat (contacts closed) check for voltage at
terminals on gas valve. If no voltage is present replace defective thermostat.
NOTE: Before replacing thermostat, be sure to check the wiring from the
furnace to thermostat for loose connections or broken wires and replace
as needed.
E. Clean or replace orifice (if okay and still no gas flow to main burners,
proceed to Step "F").
F. Replace defective gas valve.
A. Turn OFF electric power to furnace. Remove top front panel, fan shroud
and blower wheel. Refer to Wiring Diagram and check all wiring inside
junction box. Remove center front panel and check all wiring inside switch
box containing fan, limit and selector switches. Correct if necessary. If
correct, proceed to Step "B". NOTE: Selector switch used only on Models
CF50XX.
B. If burner goes OFF in less than five minutes from room temperature start,
check limit control switch. If detective, replace. NOTE: Blower should turn
"ON" within three minutes after burner is "ON" from a room temperature
start. If not, proceed to Step "C".
C. Jumper across the fan switch, turn electric power ON, the motor should
rotate. If a 2-speed motor is used. Jumper from "brown" terminal on the
fan switch to #2 (red) terminal on the selector switch, motor should rotate
on "LOW" speed. Jumper from same "brown" terminal on the fan switch
to #3 (black) terminal on the selector switch, motor should rotate on "HIGH"
speed. Replace motor if defective.
D. Jumper across fan switch, turn electric power ON, motor should rotate.
Replace motor if detective.
E. If, after checking above possibilities, problem still exists, replace fan switch.
A. Check for low gas pressure at gas valve (should be 4" W.C. for Natural Gas,
11" W.C. for propane gas. Check burner orifice).
A. Check for high gas pressure at gas valve (correct if necessary. See correct
pressure above).
B. Check line voltage to motor, if below 115 volts motor will run too slow.
C. Heated air discharging against an object causing recirculation, such as a
hall installation or a large piece of furniture within 4' of discharge.
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