Heating
SYMPTOM CAUSE REMEDY
Burners will not ignite. Water in gas line Drain. Install drip leg.
No power to furnace Check power supply fuses, wiring, or circuit breaker.
No 24-v power supply to control
circuit
Check transformer.
NOTE: Some transformers have internal overcurrent
protection that requires a cool-down period to reset.
Miswired or loose connections Check all wiring and wirenut connections.
Burned-out heat anticipator in
thermostat
Replace thermostat.
Broken thermostat wire Run continuity check. Replace wire if necessary.
Misaligned spark electrodes Check flame ignition and sense electrode positioning.
Adjust as necessary.
No gas at main burners 1. Check gas line for air. Purge as necessary.
NOTE: After purging gas line of air, wait at least
5 minutes for any gas to dissipate before attempt-
ing to light unit.
2. Check gas valve.
Inadequate heating. Dirty air filter Clean or replace filter as necessary.
Gas input to furnace too low Check gas pressure at manifold. Match with that on
unit nameplate.
Unit undersized for application Replace with proper unit or add additional unit.
Restricted airflow Clean or replace filter. Remove any restriction.
Blower speed too low Use faster speed tap if available, or install alternate
motor.
Limit switch cycles main burners Check rotation of blower, thermostat heat antic-
ipator settings, temperature rise of unit. Adjust as
necessary.
Poor flame characteristics. Incomplete combustion results in:
Aldehyde odors, carbon monox-
ide, sooting flame, floating flame
1. Tighten all screws around burner compartment.
2. Cracked heat exchanger. Replace.
3. Unit overfired. Reduce input (change orifices or
adjust gas line or manifold pressure).
4. Check burner alignment.
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