Boiler Pressure Relief Valve Keeps Going Off [5 Easy Fixes]

Over the years you are bound to struggle with your boiler pressure relief valve keeps going off. What causes a pressure relief valve to go off?

A waterlogged expansion tank, a hole in the hot water coil, a hole in the Extrol tank, a defective fill valve, and a faulty pressure relief valve are the common reasons.

boiler pressure relief valve keeps going off

Keep reading our troubleshooting guide to stop water from pouring out of the pressure relief valve. 

Table Of Contents

Boiler Pressure Relief Valve Keeps Going Off [5 Easy Fixes]

In this section, we take a deeper look at why the pressure relief valve keeps opening on the boiler and give you the answer to one of the most commonly asked questions, “How do I fix a leaking pressure relief valve?”

Note: You can also read how to convert Steam Heat To Baseboard.

1. Waterlogged Expansion Tank

This is the most common reason why your boiler pressure relief valve keeps going off.  All boiler systems for closed-loop heating must have an expansion tank. 

The volume of the system water will increase as a boiler heats it. An expansion tank uses compressed air or gas that acts as a cushion or spring against this force as water cannot be squeezed while air can.

It is crucial that the system pressure does not rise to the point where the boiler relief valve goes off, as this causes the pressure relief valve to blow off. So, a waterlogged expansion tank can be why your pressure relief valve is leaking. 


Turn your boiler off. Go to the tank and follow the pipes till you find the tank drainage valve. Go further down and you will find the shut-off valve which you need to turn off first by turning the handle down. 

Back to the drainage valve. Put a hose on the valve opening and then open the valve. Your tank is not going to drain unless air gets into it. You can find a small air vent on the side of the tank. 

Take a screwdriver to open the vent up that allows air to get in and water to start drawing. It takes 10 minutes to drain your average expansion tank which is a foot or two wide and three feet long.

Wait for the tank to drain completely before turning the drainage valve off and removing the hose.

Open the shutoff to the tank up by just a little bit. Allow the water to go back into the tank and it should actually take approximately four or five minutes.

Once that’s done, then open up all the way. You should be all done now and can start your water heater back up again.

2. Hole In Hot Water Coil

The hot water coil is what actually heats up the water in the boiler. Cold water enters the boiler through the water inlet and this coil stays immersed in the water to heat it up. When the water is hot, it again leaves through the hot water outlet. 

That is how a water heater works. When there’s a hole in this coil, the heating process doesn’t work anymore.


All you can do if there is a hole in the hot water coil is to replace it. Remove the old coil and examine. If you found a hole in it, here’s what you need to do to install a new one. 

Step 1: 

You must begin the tankless coil heater replacement by performing the unusual: read the boiler manufacturer’s directions for the unit’s safety.

The tankless coil and gasket should be unpacked. Verify the condition of each component. Remove any tie wires that may be securing the coil parts together.

Step 2: 

Empty the boiler and heating system, then allow it to cool to a temperature that is safe for use. To gain access to the spot where the tankless coil will be mounted, dismantle the boiler jacket cover panels.

Step 3:

Along with the gasket, take off the bolts or screws keeping the coil mount location cover plate in position, and throw them away. The tankless coil will typically mount on a circular or rectangular plate.

The tankless coil gasket should be placed over the coil and pressed to the inside of the mounting faceplate for the coil. Make sure the gasket and all mounting surfaces are spotless.

Step 4:

Make sure the word “TOP” (if present) is truly at the top of the coil and that any arrows that are present on the coil faceplate are pointing “up” (or in the direction indicated). Based on the coil mounting gear type, reinsert the cap screws or nuts and tighten them firmly.

Step 5:

The coil mounting fasteners, screws, and nuts should not be over tightened. If you break one off within the boiler, you’ll pay dearly for trying to remove it.

As boiler temperatures evaporate small leaks, you might just see an accumulation of mineral deposits near the coil; there shouldn’t be any standing water there.

3. Hole In Extrol Tank Diaphragm

If you have an Extrol tank instead of a bigger expansion tank, read this part carefully. Your pressure relief valve can be triggered because of a hole in the diaphragm or other flaws in your Extrol tank.

The pressure in the tank is initially precharged at 12 pounds, but this problem will raise it to around 30 pounds which sets off the pressure relief valve.


To check whether your Extrol tank is the problem, touch the top and bottom of your tank to see if anything is wrong. If the tank is working properly, it should sound different. 

It’s time to replace the tank if they all make the same sound. That is right. You can’t just drain an Extrol tank as you would with a larger expansion tank, you have to buy a new one. That’s why we are not the biggest fans of these tanks.

To replace the tank you have to first switch the heater off and go to your feed water valve and turn it off. Then locate the drain valve and put a hose on it and start draining. The pressure will drop down to 0 PSI.

You can read that on the pressure gauge. Unscrew the old tank. Be prepared for its weight. It should be close to 30 lbs. Screw on the replacement tank and your water heater should be ready to go. 

4. Defective Fill Valve

Only 12 psi is intended to pass through the pressure-reducing valve and into the boiler. Leaks may develop if the pressure is allowed to rise to 30 psi or more, which can be due to a defective fill valve.


Turn off the boiler, let it cool, and then drain some water until the pressure reaches 10 psi to see if the fill valve is the issue. If the gauge begins to rise once more, refrain from turning the boiler back on and wait.

If it does, the fill valve might be broken. In that case, you need to replace the fill valve to stop your pressure relief valve from leaking outside.

5. Faulty Pressure Relief Valve

The pressure relief valve itself can be faulty and that’s why it keeps going off. This situation is very dangerous. Every water heater should be equipped with a working temperature and pressure relief valve.

This is a crucial safety device that is mandated by all plumbing codes and it should never be removed or disabled.


You need to check to see if your pressure relief valve is faulty by conducting the following test. However, if any of the above issues are not true for your heater, chances are pretty high that it’s the pressure relief valve even without the following test.

First, you’re gonna want to grab a bucket or something small that you can get underneath the downspout coming from under the valve and place it there. And then you’ll just open the valve, let it run for about 5 seconds and then close it.

Stand back and don’t do this if you’re barefoot or wearing open-toed shoes or sandals that have water splashes out you could be burned.

Don’t be alarmed if the water flows for a few seconds after you’ve shut the valve. The water is really mostly just draining out of your long vertical pipe.

But if the water flows for more than say 10 seconds and continues to drip, then it’s time to turn off the cold water inlet for your water heater. 

Now, make sure that the pressure valve is not leaking. If it does, it is faulty and you’ll need to replace the valve. 

How To Replace The Pressure Relief Valve

It is recommended that you test your pressure relief valve once every year. And if it fails your test because it starts to leak after you’ve tested it, then it’s time to replace it. Now let’s get into the replacement procedure. 

Step 1: 

The first thing to do is to locate your Pressure relief valve. Generally, they’re going to be located on the side of your heater near the top.

You’ll notice the TMP valve because it has a little loose, floppy handle on the outside of it but tightens as you pull it. There’s a little ring with text printed on it indicating valve specifications.

Step 2: 

Read the specifications that are on the valve that’s already installed in the tank. Ideally, you should replace the valve with an exact match from the same manufacturer. 

If you cannot easily find an exact match or your specific valve is no longer available then you’ll need to match the various specifications with the valve.

Make sure your replacement valve has a BTU rating that meets your heater, is the same fitting size, and is tested to the same temperature and pressure values.

Also, make sure that the temperature probe extension length and the length of the fitting are the same.

Step 3:

Shut off your heater. Next, we need to turn off the cold water supply. There should be a valve located somewhere near the top to shut off the water supply. You want the tank water to get to a level that is below where the pressure relief valve is placed. 

Step 4: 

Next, we’ll find our drain valve and we’ll attach a garden hose to it. Make sure the other end of this hose has gone off to somewhere safe that can handle some hot water that you’re about to pour out. And then go ahead and open up your drain valve. 

Then when you open that drain valve, you’ll hear some water initially starting to rush out, but it won’t rush for very long because it’s really just the pressure that’s built up in the tank being relieved.

Go ahead and open the pressure relief valve. This will both let air into the tank so that water will drain out and you’ll be able to hear when the water level gets low enough that you can safely remove this valve.

Once the water gets down low enough water gurgling will change to more of a solid hissing sound.

Step 5:

Start by removing the downspout from the pressure relief valve. You can use a wrench for this. Once that is off, you can start loosening the pressure relief valve with the wrench until it comes off. 

Get the new valve and cover the threads with Teflon tape. You can also pipe dope to it before installing the new valve. Reinstall the downspout.

Step 6:

Remove the hose from the drainage valve. Turn on the hot side of any faucet. Then turn on the cold water supply to your heater. 

If a little bit of air comes out of your system through your faucet, there is nothing wrong with your heating system. There was air at the top of the tank and as that tank fills that air has got to go somewhere. With the new valves installed, it’s a good idea to test them.

Finally, last but not least, don’t forget to set your temperature back to your desired setting for your heater. 

Watching the video will be helpful for you.


Is a leaking pressure relief valve dangerous?

A T&P valve that drips or spills regularly is hazardous because those leaks may eventually cause the valve to clog and stop opening when it should. A highly serious BLEVE EXPLOSION could occur if a relief valve becomes clogged and refuses to open when it should.

What causes too much pressure in the water heater?

There are three potential causes if the pressure in your water heater is too high. Either the expansion tank isn’t functioning, the temperature is set too high, or there is a problem with the water heater.

Can I still use water if my water heater is leaking?

If your water heater leaks, you can still utilize the water. The leak raises the issue. Finding the leak’s precise position and the extent of its spread to your home and property’s damage or harm is challenging.

Can a hot water heater flood your house?

Your home’s basement could quickly flood if your water heater is broken or outdated. A burst or broken hose is the most frequent reason for a flood caused by a water heater.

How often should you drain your water heater?

The average homeowner should clean their water heaters every six months or so; but, if your water is exceptionally hard, you might want to flush it more frequently depending on the mineral level of the water in your home.  


Hopefully, we have adequately answered your question, “Why does my pressure relief valve keep opening?” In case you have other issues with your water heater or need some advice, you can let us know in the comment section.

About David

David is a man who loves doing research and finding out the best solution to any type of heating appliance issues like heaters and fireplaces. Whenever he finds the perfect solutions to any issues of heating appliances after doing in-depth research, he loves to share them with his readers. In fact, his aim is to help his readers to fix the issues with their heating appliances easily.More about us .

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