The Heil NUG5075BFAZ is a gas-fired and furnace equipped with a jet burner, combustion air blowers and circulating blower assisted by a fan. This model is also equipped with a gas pilot ignition with a manual control and a Honeywell thermostat. Its fan control system is designed to let the owner to choose the required furnace temperature. Heil furnaces are very reliable, but as with any other complicated appliances, they may occasionally suffer from minor breakages. Basic troubleshooting tips below will help you resolve most of such issues and save money on professional repair services.
| Problem | Solution |
|---|---|
| Pilot Light Won't light or stay lit. | Make sure the thermocouple is positioned properly in the pilot flame. |
| Another common problem is a bad regulator at the propane tank. A simple test will indicate if this is the case. Light all the stove burners and look at the color of the flame. The flames should be blue with little or no yellow color. If the flame does not change color then the regulator is probably working. A bad regulator could also cause problems with your hot water heater | |
| Fan doesn't run and no heat. | If the fan will not start you should first check that your battery is good and you have 12 volts at the furnace. You could have a tripped circuit breaker or blown fuse. |
| If the battery is good and you have electricity to the RV's heater next check the thermostat. | |
| Remove cover and look for the "anticipator" adjustment. (Note: Some new thermostats do not have an anticipator.) It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough... it normally takes our furnace 30 seconds for the fan to start once the thermostat sends a signal. | |
| If the fan starts after you move the slider then you have probably found the problem. In this case you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the plastic to melt a little and the wire to sink into the plastic so the slider no longer makes contact. It may be necessary to replace the thermostat | |
| Fan runs but no heat. | If your furnace fan starts you can assume that the thermostat is working. |
| Possible problems are insufficient air flow through the furnace a bad propane valve at the furnace or a bad regulator at the propane tank. | |
| A furnace contains an internal sail switch, that senses the air flow. If the air flow is not sufficient then the switch will prevent the furnace from igniting and the fan will run but you will get no heat. A slow motor speed could be caused by a low battery or other low voltage cause such as a bad connection in the wiring. | |
| Low air flow could also be caused by a restriction in the ventilation system. Check to see if any heat registers are closed or blocked. Some furnaces will not tolerate even a partial closure of a heat register. . | |
| If you have an electronic ignition check to see if the two contacts are touching or are too far apart. They should be about 1/8 apart |
| Status LED | DESCRIPTION |
|---|---|
| Heartbeat | Control has 24 VAC power |
| 2 Flashes | Pressure switch did not open, check for obstructed pressure tubing |
| 3 Flashes | Pressure switch did not close, or re-opened- Check for: excessive wind, proper vent size, defective inducer motor, low inducer voltages, defective pressure |
| switch, inadequate combustion air supply, disconnected or obstructed pressure tubing, low inlet gas pressure, restricted vent, condensate clogged | |
| 4 Flashes | Limit circuit fault-a limit or flame rollout is open. Check for: restricted vent, proper vent sizing, loose blower wheel, excessive wind, dirty filter, defective blower |
| motor, defective switch or connections, inadequate combustion air supply | |
| 5 Flashes | Abnormal flame proving signal-Flame is proved while gas valve is de-energized. Check for: leaky gas valve, stuck open qas valve |
| 6 Flashes | Failure to ignite or flame sense lost while running. Check for: Flame sensor must not be grounded, low inlet gas pressure, oxide buildup on flame sensor, |
| Manual valve shut off, proper flame sense microamps, gas valve defective or gas valve turned off, defective hot surface igniter, control ground continuity, | |
| Inadequate flame carryover or rough ignition, green/yellow wire MUST be connected to furnace sheet metal. | |
| 7 Flashes | Limit circuit lockout- Lockout occurs if the limit or flame rollout is open longer than 3 minutes. Control will auto reset after 3 hours. |
| 8 Flashes | Gas heating lockout-Control will NOT auto reset. Check for: mis-wired gas valve, defective control valve |
| 10 Flashes | Polarity-Line voltage, polarity reversed. |
| 1 + 2 | Blower on after power up- Blower runs for 90 seconds, if unit is powered up during a call for heat (R-W closed) or (R-W) opens during blower on delay. |
| 6 + 1 | Ignition lockout- Control will auto-reset after 3 hours. |
| LED Off | Secondary voltage fuse is open- Check for: door switch not closed, 115VAC at LI and neutral, 24VAC RED and COM BLUE, 24V Fuse 3A, short circuit in secondary voltage (24VAC wiring) |
| LED On | Control circuitry lockout- Auto-reset after one hour |
| LED SOLID | Gas valve relay stuck open- Flame sense circuit failure, software check error, reset power to clear lockout, replace control if status code repeats. |
| LED code status | Solution |
|---|---|
| HEARTBEAT (bright-dim) | Control has 24VAC power |
| 2 - PRESSURE SWITCH DID NOT OPEN | Check for: - Obstructed pressure tubing. - Pressure switch stuck closed. |
| 3 - PRESSURE SWITCH DID NOT CLOSE OR REOPENED | If LPS open longer than five minutes, inducer shuts off for 15 minutes before retry. If HPS remains open for one minute after gas valve closes (after three succesive trials), then furnace control will lockout for 3 hours before retry. Check for: |
| - Excessive wind - Proper vent sizing - Defective inducer motor | |
| - Low inducer voltage (115VAC) - Defective pressure switch | |
| - Inadequate combustion air supply - Disconnected or obstructed pressure tubing | |
| - Low inlet gas pressure (if LGPS used) - Restricted vent - Condensate drainage restricted or blocked If it opens during blower on-delay period, blower will come on for the selected blower off-delay. | |
| 4 - LIMIT CIRCUIT FAULT | Indicates a limit or flame rollout is open. |
| Blower will run for 4 minutes or until open switch remakes whichever is longer. If open longer than 3 minutes, code changes to lockout #7. If open less than 3 minutes status code #4 continues to flash until blower shuts off. Flame rollout switch requires manual reset Check for: - Restricted vent - Proper vent sizing | |
| - Loose blower wheel - Excessive wind - Dirty filter or restricted duct system | |
| - Defective blower motor or capacitor - Defective switch or connections -Inadequate combustion air supply (Flame Roll-out Switch open) | |
| 5 - ABNORMAL FLAME-PROVING SIGNAL | Flame is proved while gas valve is de-energized. Inducer will run until fault is cleared. Check for: - Leaky gas valve - Stuck-open gas valve |
| 6 - IGNITION PROVING FAILURE | Control will try three more times before lockout #6+1 occurs. If flame signal lost during blower on-delay period, blower will come on for the selected blower off-delay. |
| Check for: - Flame sensor must not be grounded - Oxide buildup on flame sensor (clean with fine steel wool). | |
| - Proper flame sense microamps (.5 microamps D.C. min., 4.0 - 6.0 nominal). | |
| - Gas valve defective or gas valve turned off - Manual valve shut-off - Low inlet gas pressure | |
| - Defective Hot Surface Ignitor - Control ground continuity - Inadequate flame carryover or rough ignition | |
| - Green/Yellow wire MUST be connected to furnace sheet metal. | |
| 7 - LIMIT CIRCUIT LOCKOUT | Lockout occurs if the limit or flame rollout is open longer than 3 minutes. |
| 8 - GAS HEATING LOCKOUT | Control will NOT auto reset. Check for: - Mis-wired gas valve - Defective control (valve relay) |
| 10 - POLARITY | Line voltage (115VAC) polarity reversed. |
| 1+2 - BLOWER ON AFTER POWER UP (115 VAC or 24 VAC) | Blower runs for 90 seconds, if unit is powered up during a call for heat (R-W closed) or (R-W) opens during blower on-delay. |
| 6+1 - IGNITION LOCKOUT | Control will auto-reset after three hours. |
| OFF - SECONDARY VOLTAGE FUSE IS OPEN | Check for: - Door switch not closed -115VAC at L1 and Neutral, 24VAC at 24VAC RED and COM BLUE, 24V Fuse 3A - Short circuit in secondary voltage (24VAC) wiring. |
| ON - CONTROL CIRCUITRY LOCKOUT | Auto-reset after one hour lockout due to |
| Problem | Solution |
|---|---|
| Furnace Not Heating | The igniter gets very hot and glows bright orange to light the gas burner. If the igniter fails or cracks, the furnace won’t heat. To determine if the igniter is faulty, remove the igniter and inspect it for cracks. If the igniter is cracked, replace it. If the igniter is not cracked, use a multimeter to test the igniter for continuity. If the igniter does not have continuity, replace it. |
| The flame sensor monitors the burner to detect whether or not a flame is present. If the flame sensor is defective, it might fail to detect a flame. If the flame sensor does not detect a flame, the control board will shut off voltage to the gas valve to prevent the furnace from heating. Sometimes, if the flame sensor is dirty, it will fail to detect a flame. Try cleaning the flame sensor with a fine abrasive pad. If the furnace still doesn’t heat, replace the flame sensor. | |
| The draft inducer motor draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the furnace to shut off after a few minutes. If the ignition process stalls, the furnace will shut off. If the draft inducer motor is at fault, replace it. | |
| Furnace is Noisy or Loud | The blower wheel blows air out of the furnace and through the house. The blower wheel is attached to the blower motor shaft with a set screw. If the set screw is loose, the blower wheel will wobble on the motor shaft, and the wheel will be noisy as it turns. Check the set screw to ensure that it is properly tightened. Next, inspect the wheel for damage. If the blower wheel is damaged, replace it. |
| Over time, the bearings in the blower motor wear out, causing the motor to become noisy. Some furnace motors can be lubricated—if your furnace motor can be lubricated, try lubricating it first. If lubricating the motor doesn’t solve the problem, or if your motor can’t be lubricated, replace the motor. | |
| The draft inducer motor draws air into the burner and then exhausts it out the flue. If the motor bearings are worn out, the motor will be loud. If the draft inducer motor is unusually noisy, replace it. | |
| Furnace Starts Then Stops | The flame sensor monitors the burner to detect whether or not a flame is present. If the flame sensor is defective, it might fail to detect a flame. If the flame sensor does not detect a flame, the control board will shut off voltage to the gas valve to prevent the furnace from heating. Sometimes, if the flame sensor is dirty, it will fail to detect a flame. Try cleaning the flame sensor with a fine abrasive pad. If the furnace still doesn’t heat, replace the flame sensor. |
| The control board regulates the power supply to all of the components of the furnace. If the control board is defective, it might not send voltage to the ignition system, causing the furnace to shut off after a few minutes. | |
| The pressure switch closes when the burner has sufficient airflow. If the pressure switch isn’t working, it might not close when the proper airflow is present, causing the ignition process to stall. If the ignition process stalls, the furnace will shut off. To determine if the pressure switch is defective, use a multimeter to test the switch for continuity. If the pressure switch does not have continuity, replace it. | |
| Furnace Blower Not Running | he blower motor blows air through the return vent, past the heat exchanger, and into the home’s venting. First, make sure that power is getting to the motor. If power is getting to the blower motor, but the motor does not run, the motor may be burned out. If the blower motor is burned out, replace it. If the blower motor hums, check the blower fan to ensure that it spins freely. If the blower fan is unobstructed but does not spin freely, replace the blower motor. |
| If the capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the capacitor has failed, inspect the capacitor. If the capacitor is bulging or leaking, replace it. The capacitor can also be checked with a meter. | |
| The control board regulates the power supply to all of the components of the furnace. If the control board is defective, it might not send voltage to the blower motor. | |
| Furnace Blower Runs All The Time | The control board has relays that regulate the voltage to each component in the furnace. If the relay that controls the blower motor fails while it is closed, it will send continuous voltage to the blower motor, causing the motor to run continuously. If the control board is at fault, replace it. |
| The wall thermostat has electrical contacts that control the power supply to the furnace. If the contact that controls the blower motor sticks closed, it will send continuous voltage to the blower motor, causing the motor to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the wall thermostat shows continuity between the (R) and (G) terminals when the thermostat is in the off position the thermostat has failed and will need to be replaced. |
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