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Water Not Getting Hot? Check the Thermocouple

Updated on October 4, 2015

The Discovery!

More than likely you are reading this article because water isn't getting hot in your shower, kitchen sink, bathroom sink, or your bath tub. Regardless, you've probably discovered this at the most inconvenient time. I discovered mine while getting ready to go to work. I was showering and was waiting for the water to get warmer which would typically take a couple of minutes; but that morning the water stayed cold. I didn't have any time to figure it out, so I toughed it out and got a good cold refreshing shower.

Troubleshooting Phase

If water isn't getting hot, it means that the water heater isn't working. The question is, what part of the water heater isn't working?

First I thought that the pilot just went out. So I tried multiple times to get the pilot to turn back on. If you've never worked on any gas-based heating system like a water heater or a gas-based fireplace, there is a pilot that is always on. This pilot is just a very small gas burning outlet that just always stays on, and is designed to light the gas that comes out of the main gas burner. This means that it will be relatively close to the burner so that it can ignite the gas that comes out of there when the heater kicks on.

Anyway, it wasn't as simple as the pilot being out. I'm no water heater repairman, so I did what most people would do--check Youtube. I found several vidoes, but found this particular one very useful:

I knew from watching the video that the pilot doesn't stay on possibly because of one or more of the following:

  • defective thermocouple
  • defective thermostat

The video showed me how to determine if the problem is the thermocouple, but I didn't have a fancy multimeter like the one used by the guy in the video. I also knew that replacing the thermostat will be more involved and possibly more expensive.

So, I came up with a hypothesis: the thermocouple is defective.

Hypothesis: The thermocouple in my water heater is defective

I'm simply going to test my hypothesis that the thermocouple in my water heater is defective. The main reason I'm taking this route is because I don't want to have to go through what the guy did to test the voltage coming out of the thermocouple. Besides, I don't have a good multimeter that can measure low level voltages. I suppose I could buy one, but why buy one when you can simply buy a thermocouple set for a few bucks. If my theory is correct, then I'm done.

I was able to buy one at Home Depot for around $15. They sell 24-Inch Universal Thermocouple at also for slightly lower price. I didn't want to wait a couple of days; that's why I got mine at Home Depot.

Extracting the Thermocouple

The video above, shows you how to extract a thermocouple. Of course, the specifics of how you do it may differ depending on your water heater model. Below is my thermocouple assembly. The thermocouple looks worn out.

thermocouple assembly
thermocouple assembly | Source

Fixed It!

I got my replacement thermocouple assembly from Home Depot for around $15 and replaced what I believe to be a defective thermocouple. I lit the pilot and it stayed on.

It's fixed!

I fixed the problem using cheap labor (me), a trip to Home Depot, and a replacement universal thermocouple. Below is a close up of the defective thermocouple.

Note that I had a feeling that it was the thermocouple for the following reasons:

  1. My water heater has been around for at least 16 years.
  2. The thermocouple is the first thing to go in a water heater, because of constant burning.

A Defective Thermocouple
A Defective Thermocouple | Source


After I discovered my water not heating up, I figured it was my water heater. I thought it was just because the pilot went out. It turns out that the thermocouple was defective. I bought a replacement assembly from Home Depot, replaced the old one, and was able to light the pilot. The water heater started working from there on. Hot don't know how much you miss it until it is gone.

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    • DDE profile image

      Devika Primić 2 years ago from Dubrovnik, Croatia

      informative and very useful.