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If the thermocouple is working, you should be able to measure 30 to 40 millivolts of voltage at the connection end of the tube when the pilot flame is on. You can test this yourself using a multimeter, but you may need a helper to keep the pilot flame burning while you do it.
How do I know if my 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 do I know if my thermocouple is bad on my water heater?
If the pilot lights but the flame goes out as soon as you release the button after holding it for 60 seconds, then the thermocouple is bad. It’s possible to replace the thermocouple without removing the burner assembly, and many repair people do this.
How do you test a thermocouple on a furnace?
Remove the thermocouple by unscrewing the copper lead and connection nut (first) and then the bracket nuts. Next, take your meter and set it to ohms. Take the two leads from the meter and touch them—the meter should read zero. Once this check is done, turn the meter back to volts.
Can a thermocouple be bad if the pilot stays lit?
The function of a thermocouple in a gas valve is to assure that an active pilot light is functioning properly to ignite any supply gas. If the thermocouple fails, for any reason, the gas flow must be shut down even if the pilot is properly lit. The function is termed a “Fail Safe” mode.
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.
How long should a water heater 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 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.
Can you bypass thermocouple on furnace?
Realistically, you have just disabled the thermocouple, but you can also reach in and unclip it from its holding bracket where it meets the pilot light. In most cases it will be held on with a gravity clip, but some are held on with a screw that must be removed with a small screwdriver.
Can a thermocouple be cleaned?
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. Cleaning a thermocouple is not a fix for an issue, such as inaccurate readings.
Why won’t my pilot light light on my furnace?
There are several possible reasons why your gas furnace pilot won’t light: an ongoing draft, a faulty thermocouple, an accumulation of dirt, or an inefficient supply.
Why does my pilot light keep going out after replacing thermocouple?
If your water heater pilot won’t stay lit even after replacing the thermocouple, you most likely have a faulty gas control valve. It is a sign that the valve is failing to open and allow gas to flow to the pilot. You could also be dealing with a tripped or faulty thermal switch.
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.
Are thermocouples universal?
Honeywell, White Rodgers, and other manufacturers make universal replacement thermocouples, usually with a 30-millivolts (mV) rating for standing-pilot furnaces. Electronic flame sensors are much less universal, and you must find the exact part specified for your furnace model.
How many MV 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.
Is a thermocouple supposed to be red?
A thermocouple is a device used to satisfy pilot safety on many 24-volt gas systems. The thermocouple is a device made up of two dissimilar metals. The flame has to envelop the upper 1/2″ to 3/8″ of the thermocouple and the tip should glow a “dull red”.
How do I know if my thermocouple is accurate?
To determine the initial accuracy of a thermocouple, you simply determine the greater of the two tolerances given. Note that standard and special tolerances for thermocouples are determined using the same method. Multiply 300°C by ±0.0075 which gives ±2.25°C.
How do you calibrate a thermocouple?
A basic calibration process involves heating water to 30°C in a thermal bath. Next, each of two multimeter leads is attached to the free end (cold junction) of the thermocouple – at this point, the multimeter should register zero microvolts as both ends are at the same temperature.
