Table of Contents
How can you tell if a thermocouple is bad?
If you can’t get the flame to light at all, and you’re sure the gas is on, there’s probably an obstruction in the pilot tube. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that’s the sign of a thermocouple malfunction.
How do you test a thermocouple?
Place one test lead on the side of the thermocouple and the other to the end that screws into the gas valve. If the thermocouple has proper continuity, a small resistance reading should be visible on the multimeter. Many multimeters also indicate continuity with an audio alert.
How many millivolts should a thermocouple produce?
A single thermocouple (C Type) is used for a standing pilot system and generally produces around 30 millivolts. This voltage is used by the gas valve to keep the pilot valve solenoid internal to the main gas valve open.
Can you clean a thermocouple?
Yes, you can clean a thermocouple, but the task must be done with a light touch. Remove the thermocouple from the process assembly, using a steel wool or emery cloth, lightly clean the tip removing any build up.
What is the resistance of a thermocouple?
A thermocouple should exhibit very low resistance. Attach the negative lead to the red wire, and the positive lead to the yellow. In this case, the reading will be about three ohms. Thus we can conclude that this sensor is a thermocouple.
What causes a thermocouple to fail?
METAL FATIGUE Like everything, thermocouples can’t stay new forever. Changes in temperature can cause regular expansion and contraction in metal, which will cause thermocouples to weaken over time. After enough time, metal fatigue can cause a thermocouple to break.
Is thermocouple millivolts AC or DC?
A device made of two dissimilar metals, which produce a DC voltage of approximately 25 – 30 millivolts when one end is subjected to heat. Several thermocouples connected together to provide a higher value of DC voltage. Typically either 250 or 750 DC millivolts.
Should thermocouple be in pilot flame?
The pilot flame should touch the thermocouple at a specific level. If the flame is blue and weak, and barely reaches the thermocouple, it needs to be stronger. If it extends well above the thermocouple, it’s too strong. Install a new thermocouple by screwing it in, heating it up a bit, and then lighting the pilot.
How do you test millivolts with a multimeter?
How to Measure Millivolts Plug the red probe into the hole marked “V” or “+” on your meter. The hole may be colored red. Plug the black probe into the hole marked “COM” or “-” on your meter. Turn your meter on. Hold the insulated handles of your probes. Read the measurement from the meter dial or the display screen.
How do you bypass a thermocouple?
To bypass the thermocouple: Move the tilts switch wire aside. Remove your thermocouple from the heater using an 8mm wrench. Pull the valve housing aside using your 13mm socket wrench. Remove the valve using your pliers. Put your thermocouple back into position.
How does a thermocouple magnetic valve work?
The thermocouple detects the heat from the pilot light, and should the pilot light go out accidentally, the thermocouple will automatically shut off the gas valve. This prevents unburned gas from flooding into the combustion chamber, where a small spark might cause an explosion.
How long should a thermocouple last?
Thermocouples can last up to 10 years if properly installed and maintained, while furnaces can last 15-20 years, although either may wear out sooner in multifamily units.
How do I know if my thermocouple is bad on my furnace?
A bad thermocouple itself can prevent a gas furnace or boiler from working – if you can light the flame at the pilot manually but then the flame goes out when you release the manual gas feed valve, the thermocouple is probably bad.
Can a thermocouple work intermittently?
In electrical circuits, the most unreliable points are electrical connections. So, if in a thermocouple circuit any of the connections suffer from corrosion or lack of intimate metal-to-metal contact, intermittent operation will result.
Can you sand a thermocouple?
Water Heater Thermocouple Cleaning in 5 Steps This is always the first step when working on a water heater. Clean the thermocouple – using the emery cloth sandpaper, sand the ends of the thermocouple and then give it a finishing touch with the lint-free cloth.
Is a flame sensor and thermocouple the same thing?
People tend to use the terms “flame sensor” and “thermocouple” interchangeably. In truth, while they basically perform the same job, they’re not the same thing. If your furnace uses an electronic controller, it’s got a flame sensor. Thermocouples are used on standing pilot furnaces that have pilot lights.
How do you clean a dirty thermocouple?
The best way to clean your thermocouple is to use either a piece of steel wool or the coarse side of a sponge to gently clean off any soot or other remnants. You can use a pencil eraser to clean between the threads of the screw that connects the thermocouple to the control valve of your system.
