How can I clean the Thermocouple on my water heater?

Oh no. Your water heater has stopped working? What’s gone wrong this time.

You might find yourself running about like mad, looking for your phone, flipping through the phone book whilst surfing the internet in desperate search for a local plumber that won’t force you to sell your home to pay for his services.

In reality, this happens really very often. We have a shower – well, try to – and find there’s no hot water. We leap out, dry ourselves from the wrath of the dreaded cold, and wrap ourselves in the warmest clothing we can find as we head off to the water heater. You notice there’s no leaks, the pressure release valves are all fine, you do all the checks – but no! Your water heater is not broken! You say. Perhaps it’s the gas supply? Perhaps the heating element has gone bust?

Nope. We usually end up replacing either the gas system or the heating element, but it still doesn’t work. But how can it not work, when you’ve just replaced the key part of the system?

Well, have you tried turning up the temperature?


Well, try it.

If you’ve managed to turn up your temperature, to, say, 50 degrees celsius (ouch, that’s a burn!) and the water coming out of the hot tap feels only mildly warm to the touch, perhaps it’s your internal temperature sensors that don’t work – your heater’s thermocouple.

If your thermocouple is broken, you’ll be annoyed you didn’t bother taking a look earlier. This is such a common mistake! If your heater can’t sense the temperature of the water it’s trying to heat accurately, it won’t know how much to heat it by. That’s why it’s essential that the thermocouple is thoroughly cleaned and maintained every few months.

But how do we clean it? Well, that’s what this article sets out to cover.

How do we actually clean the thermocouple in our water heater safely?

To carry out this process, you must be aware that there are many safety risks involved. If you’re not comfortable working with pipes and gas and electricity, or know yourself not to be very dexterous, you should always call a certified professional to carry out the job for you. This helps to almost eliminate the risk of anything going tragically wrong before your eyes.

Shut off the gas entirely

DO NOT SKIP THIS STEP. It can make the difference between a gas explosion and not a gas explosion – the difference between your life and your death.

If you’re unsure of how to go about doing this, ensure you call a licenced professional who is an expert in their field.

This is usually done by turning the valve of the pipe carrying the gas to the water heater into it’s closed position. If you’re struggling to locate this, it’s usually coloured RED or BLUE, or strongly indicated at with the words “GAS VALVE”.

Disconnect Everything From The Heater

Take a picture of the whole system or unit and all the nooks and crannies of it as well, so that you know how to put it back together once you’ve taken it all apart. Using a wrench or similar tool, unscrew each of the leads going into the tankless water heater. Place these safely on the ground. Of course, always ensure that there is no water in the actual tank before you do this, if you even have a tank. You really don’t want hot water spilling everywhere, causing property damage.

Clean The Thermocouple with a Fine Sandpaper

When we say delicate sandpaper, we mean delicate sandpaper, so don’t even begin to reach for your heavy-duty wood and metal sandpaper, unless you’ve got a few centimetres of filth all over the thermocouple.

If you do have to disassemble anything to reach the actual thermocouple, you’re going to want to really consider taking a picture in case you don’t know how to put it all back together again. This way, you can save yourself a lot of money by having to call someone to fix it.

And While You’re at it – Clean the rest of the unit

This is a sort of “trick” step. Of course, this isn’t at all essential, but why not clean the rest of it? It will ensure that you don’t have to touch it again anytime soon, and you might as well tick off your maintenance. In fact, at this stage, many people detect problems they didn’t know they had before. This can prevent those problems from developing into something greater, and something far more painful to fix in the long run.

Whilst you’re there, clean it all!

Using the photo you took in the first step, re-attach the pipes and power source

There usually won’t be more than three things you’ve got to connect – your water inlets, water outlets and your gas/electrical input, and potentially your venting as well.

Now that you’ve cleaned it all and are ready to see it working again, simply connect all that needs connecting, referring to the picture again if you need it, and clean up the area around you. Check there are no parts you forgot to screw back on.

Often, people forget their o-rings at this point, and their water will leak because their system isn’t properly sealed.

Power it up

You’ve finished everything! That’s fantastic. Now all you need to do is get the gas lit and running, and you should find that everything is working as it was before.

All that’s left to do now is adjust the temperature to your desired level, and let the unit heat up for a few minutes. During this time, double check there’s nothing on the floor surrounding you, and ensure all the valves that need to be open are actually open.

Congratulations, you’ve just fixed your heater by yourself!

About the author

Steve Bates

Hi, I'm Steve and I currently reside in Chicago, Illinois. Although for most of the last 20 years I was a partner in a HVAC company down in Austin, Texas.

I understand the frustration involved with dealing with water heater repairs and replacing or upgrading to a new, more efficient model.

My aim is offer some basic advice on fixing home hot water systems. And if a repair isn't possible, then to make the process of selecting a new water heater – be it gas or electric - as simple as possible.

So that you can save money and have a safe and reliable hot water system in your home for many years to come.