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Large Unit Heater
24
Operating Instructions and Owner’s Manual
Symptom Possible Cause Corrective Action
The draft inducer motor
does not turn on
1. The air circulating fan does not turn on immediately.
2. The heater does not have 120 VAC at the main power
connection.
3. There isn’t 24 VAC across the ‘R’ and ‘C’ terminals
4. There isn’t 24 VAC across the ‘W’ and ‘C’ terminals.
5. The control board is not sending 120 VAC to the draft
inducer motor.
6. The draft inducer impeller is obstructed or locked up.
7. After checking the above, the draft inducer impeller is not
obstructed or locked up.
8. The pressure switch is stuck in the closed position.
9. The two flame roll out switches and the tube temperature
limit switch are closed.
10. The two flame roll out switches and the tube temperature
limit switch are not closed.
1. Limit switch is open or pressure switch is
stuck closed. Find faulty switch and repair.
2. Find source of electrical problem.
3. Check internal transformer.
4. Repair thermostat or thermostat wiring.
5. Check power supply, and if there is power,
replace control board.
6. Remove obstruction.
7. The draft inducer motor is faulty and must
be replaced.
8. Pressure switch is faulty.
9. Replace control board.
10. Reset or replace faulty limit switch.
The pressure switch indica-
tor light does not turn on
1. The inlet or outlet of the heater is obstructed or the vent
exceeds the recommended lengths.
2. Loose wiring or restrictions in the hose connection to the
pressure switch.
3. Replace pressure switch after verifying:
• Heater, blower, and venting are clean and free of
obstructions.
• The allowable vent length is not exceeded.
• There is not a negative pressure experienced at the area
of intake (e.g., high winds, attic space, tightly sealed
building).
1. Remove obstruction or correct vent lengths.
2. Replace wiring or hose connections.
3. Replace pressure switch.
The control board does
not send spark to the
electrode
1. The electrode appears to be physically damaged.
2. There is no continuity by temporarily disconnecting the
igniter wire from the control board.
3. There is continuity by temporarily disconnecting the
igniter wire from the control board.
1. Replace electrode.
2. Replace electrode.
3. Replace control board.
The gas valve does not
open
1. The inlet pressure to the heater is not within the minimum
and maximum allowable range as per the rating plate.
2. The wires to and from the gas valve are not properly
connected.
3. The voltage on V1 and V2 terminals on control board
during trial for ignition is not 24 VAC during the spark
sequence.
4. The voltage on V1 and V2 terminals on control board
during trial for ignition is 24 VAC during the spark
sequence.
1. Adjust inlet pressure.
2. Correct wiring.
3. Check for flash codes on the control board.
Replace the control board.
4. Gas valve is faulty. Replace the gas valve.
The burners do not ignite 1. The gas supply valve mainstream to the unit heater is not
open.
2. The inlet pressure to the heater is not within the minimum
and maximum allowable range as per the rating plate.
3. The gas lines are not purged of all air.
4. The heater’s gas type does not match the gas supplied.
5. The manifold pressure doesn’t match with the specified
pressures per the rating plate.
6. Check control board for flash codes.
1. Turn on gas supply line.
2. Adjust inlet pressure.
3. Purge gas lines.
4. Contact local representative or factory.
5. Adjust pressure or replace gas valve.
6. Consult factory.
TROUBLESHOOTING GUIDE
NOTICE: Bypassing any switch is intended for testing purposes only. Do not leave switch bypassed during normal operation or the heater’s built-
in safety mechanisms will be compromised.
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