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Table 19 — Heating Service Analysis
LEGEND
GR —
Ground
PROBLEM CAUSE REMEDY
Burners will not ignite.
Misaligned spark electrodes. Check flame ignition and sensor electrode positioning. Adjust
as needed.
No gas at main burners. Check gas line for air; purge as necessary. After purging gas
line of air, allow gas to dissipate for at least 5 minutes before
attempting to relight unit.
Check gas valve.
Water in gas line. Drain water and install drip leg to trap water.
No power to furnace. Check power supply, fuses, wiring, and circuit breaker.
No 24 v power supply to control circuit. Check transformer. Transformers with internal overcurrent
protection require a cool-down period before resetting. Check
24-v circuit breaker; reset if necessary.
Miswired or loose connections. Check all wiring and wire nut connections.
Burned-out heat anticipator in thermostat. Replace thermostat.
Broken thermostat wires. Run continuity check. Replace wires if necessary.
Inadequate heating.
Dirty air filter. Clean or replace filter as necessary.
Gas input to unit too low. Check gas pressure at manifold. Clock gas meter for input.
If too low, increase manifold pressure or replace with correct
orifices.
Unit undersized for application. Replace with proper unit or add additional unit.
Restricted airflow. Clean filter, replace filter, or remove any restrictions.
Blower speed too low. Install alternate motor, if applicable, or adjust pulley to increase
fan speed.
Limit switch cycles main burners. Check rotation of blower, thermostat heat anticipator settings,
and temperature rise of unit. Adjust as needed.
Too much outdoor air. Adjust minimum position.
Check economizer operation.
Poor flame characteristics.
Incomplete combustion (lack of combustion air)
results in:
Aldehyde odors, CO, sooting flame, or floating
flame.
Check all screws around flue outlets and burner compartment.
Tighten as necessary.
Cracked heat exchanger.
Overfired unit — reduce input, change orifices, or adjust gas
line or manifold pressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Burners will not turn off.
Unit is locked into Heating mode for a one minute
minimum.
Wait until mandatory one minute time period has elapsed or
power to unit.