14
Unitary Products Group
035-14289-000 Rev. A (0701)
PROBLEM
POSSIBLE CAUSE
REMEDY
Furnace will not start
Thermostat
not calling for heat
Check thermostat and adjust. Also, check thermostat for accuracy; if it is a
mercury switch type, it might be off level.
No power to furnace
Check furnace switch, main electrical panel furnace fuse or circuit breaker.
Also look for any other hand operated switch, such as an old poorly located
furnace switch which was not removed during furnace replacement.
Thermostat faulty
Check reset button on protector relay. Remove thermostat wires from pro-
tector relay terminals TT. Place a jumper across TT. If furnace starts, replace
thermostat, thermostat sub-base (if equipped), or both.
Protector relay faulty
Check reset button on protector relay. Remove thermostat wires from pro-
tector relay terminals TT. Check for 24v across T.T. If no voltage is present,
check for 115v to protector relay. If 115v is present, replace protector relay.
Photo cell wiring
shorted or room light
leaking into photo cell
compartment
Check photo cell (cad cell) wiring for short circuits. Also check for room light
leaking in to cad cell compartment. Repair light leak if necessary.
Open safety switch
Check for open limit or auxiliary limit, open door switch (if equipped). Also,
check internal wiring connections, loose connectors, etc.
Furnace will not start
without first pushing
protector relay reset
button
(Happens on a
frequent basis)
No fuel oil
Check fuel oil supply. Check that all hand operated fuel oil valves are in the
open position. Fill oil storage tank if necessary.
Clogged nozzle
Replace nozzle with high quality replacement. Use rating plate or table in
this manual as a guide.
Clogged oil pump filter
Replace oil tank filter or in-line filter if used.
low oil pump pressure
Connect pressure gauge to oil pump. Adjust pump pressure, or replace oil
pump if necessary. Ensure that erratic pressure readings are not caused by
defective fuel oil lines.
Air getting into fuel oil
lines, or fuel oil line
dirty, clogged or in
some manner defective
Check oil lines, Replace any compression fittings found with high quality
flared fittings. Check for any signs of oil leaks. An oil leak is a potential
source of air or contaminants.
Defective burner motor
Check burner motor. If burner motor is cutting out on over-load, determine
why. Replace, if necessary
Furnace starts, but
cuts out requiring
manually resetting the
oil protector reset but-
ton
Photo Cell (Cad Cell)
defective
If cad cell is dirty, clean it. (Determine why cad cell is getting dirty). If cad cell
is poorly aimed, realign it. NOTE: The photo cell should have a resistance of
100 K ohms in absence of light; a maximum of 1500 ohms in the presence
of light. Ensure that room light is not leaking into the cad cell compartment.
No fuel oil
Check fuel oil supply. Check that all hand operated fuel oil valves are in the
open position. Fill oil storage tank if necessary.
Clogged nozzle
Replace nozzle with high quality replacement. Use rating plate or table in
this manual as a guide.
Clogged oil filter
Replace oil tank filter or in-line filter if used.
Low oil pump pressure
Connect pressure gauge to oil pump. Adjust pump pressure, or replace oil
pump if necessary. Ensure that erratic pressure readings are not caused by
defective fuel oil line.
Air getting into fuel oil
lines, or fuel oil line
dirty, clogged, or in
some manner defective
Check fuel lines. Replace any compression fittings found with high quality
flared fittings. Check for any signs of oil leaks. any oil leak is a potential
source of air or contaminants.
Defective burner motor
Check burner motor. If burner motor is cutting out on over-load, determine
whey. Replace if necessary.
Water or contaminants
in oil.
Drain fuel oil storage tank, replace fuel oil. (Consult with fuel oil supplier).
Frozen oil line
Gently warm oil line. Insulate oil line. (Outdoor piping size may require in-
creased diameter.
SYSTEM TROUBLESHOOTING
