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I
POSSIBLE CAUSES
SYMPTOMS CHECK/REMEDIES
Pressure switch won't close
11. Unit does not operate Check for blocked combustion
air pipe
Check for inoperative Induced
draft blower; replace if necessary
Checked for blocked drain
Check for blocked vent pipe
Restriction of combustion air or Check piping tables for: improper
vent piping pipe length, too many elbows,
proper terminations
No gas supply Turn on gas supply,
check all valves
Inoperative gas valve Test and replace as necessary
Leaking induced draft fan motor gasket Replace gasket
Integrated furnace control board Unit in soft lockout, test and
determine cause
Pressure switch remains open Check, replace if necessary
or closed
Check for blocked drain
Open over temperature switch Reset, test and determine cause
Check for blocked drain
Damaged heat exchanger
12. Uneven temperature control Adjust dampers to balance system
Unbalanced air distribution system
Improper thermostat location Relocate thermostat
Improper heat anticipator setting Adjust heat anticipator,
add 100 Ohm, 10 watt resistor
or isolation relay
Oversized unit Check heat load calculation
13. Burner does not maintain flame Incorrect polarity of incoming Check and correct
electrical power
Check and correct
Incorrect gas input
Replace flame sensor
Damaged flame sensor
Check sensor wire, wiring
harness and junction plugs
Damaged sensor wiring
Incomplete combustion Check piping tables for correct
pipe sizes and number of elbows
Check for recirculation of
combustion gases
Check and correct as necessary
Pressure switch opening
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