SYMPTOMS POSSIBLE CAUSES CHECK/REMEDIES
9. Insufficient heat
Unit undersized
Recalculate heat loss
Blower running backwards Check motor rotation and
correct/replace motor if necessary
Limit control cycling Check for proper air flow
Check for overtiring
Unit underfired Check/adjust gas pressure
Improper burner orifices
Replace with proper burner orifices
Low airflow
Check filters; check blower speed;
check system static pressure
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Poor combustion Check for sufficient combustion air
or blocked pipe
Check for combustion gas
recirculation
Check for proper orifices, refer to
orifice size table
Faulty thermostat Check heat anticipator setting;
add 100 Ohm, 10 watt resistor or
isolation relay if necessary
Replace if necessary
10. Delayed (noisy) ignition Damaged igniter
Check and replace if necessary
Incorrect gas pressure Check and adjust manifold
pressure
Incorrect burner orifices Check and replace orifices if
necessary; check orifice table
Damaged burner(s) Replace
Trap not filled with water Fill trap
11. Unit does not operate Check power supply Check for: no 120 volt power;
blowers fuse/open circuit breaker;
open blower door switch
Incorrect incoming power polarity Check power polarity and correct
if necessary
Loose electrical connections
Tighten all connections
Inoperative thermostat Replace thermostat
Blown transformer fuse Replace fuse and retest
Inoperative transformer Check for 120 volts to primary
winding; replace if 120 at primary
and no 24 volt secondary
Inoperative igniter(s); or high
resistance igniter
Check igniter wiring;
replace igniter
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