Provincial
Well-known member
I have a Reznor RA140 waste oil heater in my shop. It has been very reliable for the 15 years I've used it. It has a system that preheats the oil before sending through the nozzle to be burned. This involves three electrical heating elements, two temperature sensors, a solenoid fuel valve, and a small air compressor. These all work with a control unit that senses the flame and shuts down the burner if it doesn't fire or goes out. It is all connected together with individual wires routed through flex conduit, a 20-post terminal block in the main box and a 10-post terminal block at the burner junction box.
The other day one of the temperature sensors failed. It is the one that keeps the nozzle block from overheating, and is normally "closed" and conducting 120 volts in order for the unit to run. Since it wouldn't conduct voltage, the unit wouldn't start. I used the factory service manual to troubleshoot the problem, and bought a new sensor. Tuesday I dismantled the burner, replaced both sensors, one heating element, an insulating sleeve, and the nozzle on the nozzle block. I figured that this would give me years of service in the future. Then I reassembled the burner unit, let the heaters warm up the oil, bled the air out of the system, and started it up.
It wouldn't start. Normally, the burner fan runs before the fuel reaches the nozzle, but the fan motor wouldn't run. I could hear a buzzing sound. Following the troubleshooting manual, all other problems were eliminated, and the manual said to replace the burner motor. Being experienced in troubleshooting things in general, and somewhat "frugal," I decided to test the motor with a separate 120V power source. It operated normally. This told me that something was amiss in the wiring.
I probed the terminals with my multimeter, looking for issues. Voltage seemed normal, even to the motor. I then tested all the neutral terminals against the neutral feed from the power source. I found that the burner terminal block had 158 ohms resistance back to the main box. After removing, cleaning, and replacing the wires at the burner terminal block, resistance dropped to almost zero, and the unit began operating normally.
Always check a "failed" part separately before discarding it.
Always suspect poor connections or wiring when troubleshooting, especially grounds in DC systems and Neutrals in AC systems.
The other day one of the temperature sensors failed. It is the one that keeps the nozzle block from overheating, and is normally "closed" and conducting 120 volts in order for the unit to run. Since it wouldn't conduct voltage, the unit wouldn't start. I used the factory service manual to troubleshoot the problem, and bought a new sensor. Tuesday I dismantled the burner, replaced both sensors, one heating element, an insulating sleeve, and the nozzle on the nozzle block. I figured that this would give me years of service in the future. Then I reassembled the burner unit, let the heaters warm up the oil, bled the air out of the system, and started it up.
It wouldn't start. Normally, the burner fan runs before the fuel reaches the nozzle, but the fan motor wouldn't run. I could hear a buzzing sound. Following the troubleshooting manual, all other problems were eliminated, and the manual said to replace the burner motor. Being experienced in troubleshooting things in general, and somewhat "frugal," I decided to test the motor with a separate 120V power source. It operated normally. This told me that something was amiss in the wiring.
I probed the terminals with my multimeter, looking for issues. Voltage seemed normal, even to the motor. I then tested all the neutral terminals against the neutral feed from the power source. I found that the burner terminal block had 158 ohms resistance back to the main box. After removing, cleaning, and replacing the wires at the burner terminal block, resistance dropped to almost zero, and the unit began operating normally.
Always check a "failed" part separately before discarding it.
Always suspect poor connections or wiring when troubleshooting, especially grounds in DC systems and Neutrals in AC systems.