How do you test a thermocouple on a hot water heater?

If the pilot light doesn’t stay lit, check the gas water heater thermocouple by keeping the pilot button depressed. Measure the current by using the multimeter device, set on millivolts. One probe of the meter should be connected to the copper sheath of the thermocouple and the other to the gas valve.

Test thermocouple using multimeter: Thermocouple has 2 ends: one end screws into gas valve, other end is positioned in the pilot flame.

  1. Light pilot. Hold down pilot button for 30 to 60 seconds.
  2. Relase pilot button.
  3. If pilot light goes out when button is released, then thermocouple is most likely at fault.

Also, can you clean a thermocouple on a water heater? Cleaning Steps Turn off the power to your hot water heater so that you do not risk becoming injured while cleaning the thermocouple. The ends of this piece may be corroded, preventing power from reaching the pilot light. Sand the ends of the thermocouple with emery cloth sandpaper.

Keeping this in consideration, how do you check a thermocouple?


  1. Locate the pilot light controls on the gas valve.
  2. Turn the pilot light on for 30 seconds.
  3. Release the button to see if the pilot light goes out.
  4. Turn off the gas supply to test the thermocouple again.
  5. Count to 20 and wait for the pilot light to go out.
  6. Listen for clicking near the gas valve.

How do you troubleshoot a thermocouple?

Before the test, turn off the gas supply because you must first remove the thermocouple. 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.

How do you know if you have a bad thermocouple?

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 long should a thermocouple last?

The thermocouple unwinds and switches on the fireplace. Thermocouples are rigorously tested and should last for years. Indeed, experts believe a four-year check cycle is all that is needed to make sure things are functioning properly.

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.

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 you clean a thermocouple?

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.

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 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.

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.

What color is positive on Type K thermocouple?

Type K thermocouples generally will work in most applications because they are nickel based and have good corrosion resistance. 1. Positive leg is non-magnetic (Yellow), negative leg is magnetic (Red).

How many types of thermocouples are there?

Thermocouple Grade Wire Calibration Type Temperature Range K 32 to 2282°F 0 to 1250°C E 32 to 1652°F 0 to 900°C T 32 to 662°F 0 to 350°C R or S 32 to 2642°F 0 to 1450°C

Does a thermocouple need to be grounded?

Should I use a grounded or ungrounded thermocouple? A thermocouple is called “grounded” when the sensing junction is connected (physically and electrically) to the metal case. There are advantages and disadvantages but generally ungrounded thermocouples are preferable, providing a slower response time is acceptable.

What voltage should a thermocouple produce?

The higher the temperature, the higher the voltage produced by the thermocouple. (It is somewhat misleading to use the terms “high” and “voltage” in this context, since the voltage across a common, J Type thermocouple is about 1.0 mV at a room temperature of 68°F and about 1.9 mV at body temperature, 99°F).

Can a thermocouple work intermittently?

a safety device that has started to go bad, or has failed permanently. In this client’s case, the thermocouple was initially working intermittently, and then finally failed. This allowed the gas to flow long enough to heat up the thermocouple and generate some electrical current flowing back to the gas valve.

How much voltage does a thermocouple generate?

The normal millivolt output is 25 to 35 millivolts; on some, you may even get up to 35. The other part of this safety pilot system is the electromagnet (power unit). It is if you will the LOAD and we can say the thermocouple is the SOURCE.