THB & TLB
Oil Furnaces
–
Furnace Manual
18
670-000-005/1010
9
Troubleshooting
Check 120 volt supply to furnace. If there is no supply
To successfully service the oil furnace, you must
voltage, check fuses and service switch. CAUTION :
have these instruments :
When testing electrical equipment, always follow
smoke tester
standard electrical safety procedures.
carbon-dioxide (CO
2
) or oxygen (O
2
) analyzer
draft gauge (scale should read from -.01” w.c. to -.25” w.c.)
volt/OHM/milliamper multimeter
pressure gauge capable of reading 0-150 lb/sq. inch (for oil only)
Be familiar with these instruments as well as the burner
manufacturer's recommended settings.
Before beginning these troubleshooting procedures, ALWAYS :
Make sure thermostat is calling for burner operation.
Check oil supply and make sure all valves are open.
Symptom – Burner
Check fuses and make sure service switch is
on.
Check for voltage from primary relay to burner
motor. Make sure the primary relay has not
locked out on safety.
Check for line voltage into furnace junction
box.
Make sure the thermostat is calling for heat
and that the wiring to the thermostat is correct.
If the primary relay control is not popping out
the reset button, measure the milliamperage at
the thermostat and set the heat-anticipator
accordingly. Also check wiring from the
thermostat to the burner.
Check the alignment of the cad cell to assure
it is aimed at the fire.
Check nozzle and electrode position.
Check ignition transformer output
(Reference burner manufacturers
instructions).
Check tube insertion and alignment.
Check nozzle and electrode position
(Reference burner manufacturer's
instructions).
Replace nozzle.
Check
pump
pressure
(varies
with
manufacturer and application; see burner
manual).
Check overfire draft.
1. Remove CAD cell leadwires from the f-f
terminals on the primary safety control, then
start burner. Shortly after burner starts, place
a temporary jumper between terminals f-f.
Connect ohmeter across CAD cell leadwires-
resistance should be under 1,600 ohms.
3. With burner off, check dark cell resistance
across CAD cell leadwires. Resistance should
be
greater
than
20,000
ohms.
If
cell
resistances are different from above, recheck
wiring and location of cell, etc. If necessary,
replace plug-in portion of cell.
2. Stop burner and remove temporary jumper.
Possible corrections :
To check CAD cell operation, use the
following procedure :
Burner motor does not start.
Unable to achieve clean combustion
by setting air adjustments.
Burner short cycles or locks out on
primary relay safety.
Symptom – Furnace blower
Furnace blower will not start.
Check wiring from Fan and Limit control. See
if blower motor will run when it is switched on
manually at the thermostat sub-base (if sub-
base is installed).
Check for 120V to the blower motor. If
present, replace motor.
Blower short cycles on limit control.
Return ducts may be undersized.
Possible corrections :
Adjust fan "off" setting to 90
o
and adjust fan
"on" setting to 110
o
.
Blower cycles on and off after the
burner has shut down.
Summary of Contents for THB High Boy series
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Page 36: ...THB TLB Oil Furnaces Furnace Manual X40108 Rev J ...
