How does a furnace thermocouple work?

The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. If the pilot light goes out, the loss in heat causes the voltage between the two pieces of metal to drop, and this shuts the valve and reduces the combustion risk.

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In respect to this, where is the thermocouple on a furnace?

The thermocouple is a gas furnace component located near the pilot light burner. It is a safety device that shuts off the gas if the pilot light goes out or the electric igniter fails. If the pilot light won't stay lit, the thermocouple may be faulty and should be adjusted or replaced.

Beside above, how do I know if my thermocouple is bad on my furnace? 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.

Similarly, you may ask, how does a thermocouple work on a gas valve?

A thermocouple is a device made of two different metals which creates a small electrical charge when heated at one end by the gas pilot. This small charge causes an electromagnet inside the gas valve to open and allow gas to flow to the main burners.

How long does a thermocouple last?

Thermocouples can last several years, but they don't typically last as long as the furnace itself. If the pilot remains lit, but the main furnace doesn't stay lit, it's time to replace the thermocouple.

Related Question Answers

What causes a thermocouple to fail?

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. If thermocouples start to give out unusual readings, it may be suffering from metal fatigue.

Can a thermocouple be cleaned?

If the Thermocouple is faulty it will cause the unit to shut down. How to clean? Remove Thermocouple from pilot assembly, using steel wool or emery cloth to lightly clean the tip removing any soot or build up that might have accorded due to an improper pilot flame.

How much does it cost to replace a thermocouple on a furnace?

Cost to Replace a Thermocouple on a Furnace Replacing a thermocouple costs $150 to $250, mostly due to labor time. On older models without an ignitor, it checks to make sure your pilot light is lit. If it's not, it'll shut the gas off.

How do you clean a thermocouple on a furnace?

Process

1. Turn off the gas leading to your furnace.
2. Open up furnace cover and look at the pilot light and thermocouple.
3. Set both pieces on the towel (or some other soft surface which you can clean easily later.
4. Use the wire brush to scrub the pilot light and thermocouple.

Can you fix a thermocouple?

A burned out or broken thermocouple should be replaced. To replace a thermocouple: Step 1: Unscrew the copper lead and the connection nut inside the threaded connection to the gas line. Step 2: Under the mounting bracket at the thermocouple tube, unscrew the bracket nut that holds the tube in place.

What is the purpose of a thermocouple?

A thermocouple is a safety device that's used to detect whether or not your furnace's pilot light is lit. It contains a metal rod that is placed very close to your pilot light's flame. When your pilot light is lit, the heat from the flame sends a voltage through the thermocouple that keeps the gas line open.

Are thermocouples universal?

Universal Thermocouples. Universal thermocouples, as the name implies work on most water heaters. They are available online and in home supply stores for a reasonable cost. The length and the thread type are the two concerns when purchasing one.

What causes a gas valve to go bad?

The valve itself may have simply worn out or may be damaged due to basement seepage or submersion. Alternately, one of the electronic gas ignition components or a glitch in the safety circuit may be to blame. If your furnace has a standing pilot light, the thermocouple could be worn out.

What does a thermocouple look like?

The thermocouple looks like a piece of metal tubing smaller than a soda straw. To find it, first locate the gas control box. This is the box that the main gas line enters, where you turn the gas on in the furnace. The other end of the thermocouple sits in the flame of the pilot light.

How much does a thermocouple cost?

The No. 1 cause of pilot lights that won't stay lit is a worn-out thermocouple. It's easy to replace and a new one costs $5 to $10. Rather than trying to unfasten the thermocouple inside the water heater's burning chamber, it's easier to remove the whole burner and thermocouple assembly.

How do you test a gas valve?

How to Check the Furnace Gas Valve With a Multimeter

1. Turn off the furnace at the wall control.
2. Take out the bolts in the service panel on the side of the furnace using a nut driver.
3. Pull the wires off the gas valve terminals.
4. Turn the test control on the multimeter to "mV," which stands for millivolt.

How close should the thermocouple be to the pilot light?

about 1/2 inch

How do you replace a thermocouple on a furnace?

Replacing a Thermocouple

1. Shut off the gas and electrical power to the furnace.
2. Remove the furnace's access cover.
3. If the furnace has been running, wait 30 minutes for the thermocouple to cool completely.
4. Unscrew the nut that holds the thermocouple end fitting into the gas control valve, using an open-end wrench.

How much should a plumber charge to replace a thermocouple?

Thermocouple Replacement - $20-$150 Calling a professional plumber to install a new thermocouple should only be up to $150. If you do the work yourself, you will only pay the price of the part which is about $20.

Can you test a thermocouple?

MultiMeter Thermocouple Test Procedure First, remove the thermocouple. Secondly, turn on the meter and set it to Ohms. Touch the two leads together from the meter, and you should get a reading close to zero. With the leads apart, you will read infinity.

Can a thermocouple be bypassed?

Bypassing the thermocouple would make it no more dangerous than any propane grill. It's not going to make it explode. The only thing it would prevent is losing a tank of propane into the atmosphere if the flame happened to go out because the valve wouldnt close.

Will a pilot light stay lit with a bad thermocouple?

A thermocouple senses the heat of the pilot and allows gas to flow to the burner. A bad thermocouple will shut off gas to both the pilot and the burner so the pilot light won't stay lit.

Why does the flame on my furnace keep going out?

Your furnace has a limit switch that keeps it from running if the heat exchanger is too hot. Dirty filters, closed or blocked vents and other blockages in airflow are common causes of an overheated furnace. A direct ignition furnace has flame sensor over the burner that shut off the gas if it doesn't sense a flame.

Why does my pilot light go out when I release the pilot light knob?

The most likely of those is that the thermocouple needs to be replaced. The button you press to light the pilot bypasses the thermocouple. When you release the button, the thermocouple ensures that unburned gas doesn't get released by shutting off the gas when it's not heated by the burning pilot light.