What Causes A Water Heater’s Relief Valve To Discharge Water?

So you went to grab some things from your basement only to find it flooded with water.

The first thing that comes to your mind is the water heater. It’s leaking again from the relief valve.

But why is the relief water discharging water in the first place?

If a water heater’s discharge valve is leaking, it can be either excessive temperature, excessive pressure, or just a leak in the relief valve itself. In the case of both temperature and pressure, the relief valve is doing its job, preventing an explosion. But you might want to get the pressure valve fixed if it’s leaking.

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Reasons why a heater’s relief valve discharges water

Most standard indoor water heaters have a relief valve. This purpose of the relief valve is to discharge water in two cases:

  1. Excessive water temperature
  2. Excessive water pressure

When either of these takes place, the relief valve is activated, and the excess hot water flows out the relief valve.

But this is not always the case. Sometimes, there’s a third reason why water discharges from the relief valve, and that is that if your relief valve is faulty or not properly sealed. In that case, you will need to replace the relief valve completely,

Here are some of the ways you can test what’s causing the relief valve to discharge water:

Diagnosing the cause of relief valve leak

As we mentioned earlier, there can be three reasons for this. Here are simple ways you can test it:

1. Excessive Temperature

Testing the temperature with a thermometer

The very first test you should be doing is of the water temperature. To do this, simply let the heater run and open a hot water tap anywhere in the house for a good 2 to 3 minutes.

After this, place a thermometer in the running water for 10 to 20 seconds and read the temperature. If your water temperature is 210 °F or higher, then it’s likely that your relief valve is discharging water due to the water overheating.

But if the water temperature is below 210 °F, then there might probably be a problem with the water pressure or the relief valve itself.

2. Excessive Pressure

Using a water pressure gauge

Using a water pressure gauge is a simple method of determining whether excessive pressure is causing the relief valve to discharge water.

To do this, simply go to your local plumbing store and buy a threaded pressure gauge. These are usually accurate enough for our purposes here.

Once you have the pressure gauge, simply attach it to a hose bib around the house. The cold or hot water tap in the laundry room is a good place to start.

Normal water pressure falls between 40-80 PSI with no other taps running. Double-check the reading by attaching the pressure gauge to another hose bib and test the water pressure there.

If the pressure is less than 80 PSI, it’s all well and good. But if it’s more than 80 PSI, then you’ve got a problem.

Testing for intermittent pressure increase

Here’s another scenario:

If your water pressure is closer 80 PSI, your relief valve can still be releasing water. In this case, it could be that your water system suffers from an intermittent or periodic increase in pressure.

So how do you diagnose this issue? Empty your heater’s hot water supply by running all the hot water by taking a shower or a bath, or you could simply open all the hot water valves in your home to exhaust the hot water.

After the water turns cold, close off all the taps and wait for the heater to start heating the cold water again. Run the water again and check the reading on the pressure gauge. If it’s still between 40-80 PSI, the pressure isn’t the problem here.

3. Faulty Heater Relief Valve

Faulty relief valve

If the problem is neither with your water temperature or pressure, then you might have a faulty relief valve. Sometimes, the relief valve isn’t installed correctly, or the seal or other parts are failing with time, causing the relief valve to begin dripping.

In the case of both excessive pressure and temperature, the relief valve tends to discharge water in large quantities. If the fault is with your relief valve, there will likely be a slow and gradual drip not from the relief valve, but its connection to the heater.

Wrong relief valve

Another possibility is that you’ve got the wrong valve installed. A standard Temperature and Pressure Relief Valve (TPRV) for water heaters releases water at 150 PSI or 210 °F.

If you’ve accidentally installed a boiler relief valve or some other valve, it will go off at a lower pressure and will drip under the wrong conditions.

Fixing a heater’s relief valve

How you fix your water heater’s relief valve depends on what’s the issue causing the leakage. In some circumstances, a few tools from your local hardware store and your storeroom would be enough to fix it.

However, if the issue is beyond your understanding and you aren’t comfortable with plumbing, you’ll need to contact a plumber to do the work.

Fix for water temperature issues

If the relief valve is discharging water due to excessive temperature, then the relief valve itself is functioning as it should and doesn’t needs replacement.

You could try to lower the temperature or contact a plumber to determine the solution if the relief valve is discharging water too frequently.

Fix for water pressure issues

There isn’t a single solution for excessive water pressure. If the increase in pressure is constant, like in the first pressure test, then you need to install a new pressure regulator.

Pressure regulators can be easily found in most hardware stores and can also be installed by yourself if you’ve got some expertise. Otherwise, you could just call your plumber to fix it for you.

However, if you have intermittent pressure increases, the best fix would be to get an expansion tank installed. Here’s the science behind an expansion tank. When the heater starts heating water after some hot water is used up, some excess hot water flows back into the main inlet pipe as it expands, causing the water pressure in the pipelines to rise as it has nowhere to go.

An expansion tank provides the excess hot water that flows back into the inlet pipe, a place to go preventing the pressure from becoming excessive and water from discharging via the relief valve.

Fix for relief valve issues

After a time, heater relief valves corrode or leak due to a faulty seal. In this case, you can quickly get a new relief valve from a local hardware store and replace it on your own with a few tools.

When doing this, just make sure that the new relief valve you’re buying is compatible with your water heater and rated for 150 PSI and 210 °F. If you’re hesitant about replacing the valve yourself, you can also get them fixed by your plumber.


Is a leaking relief valve dangerous?

If your T&P relief valve is leaking, it means there is something wrong with it. Replacing a T&P valve usually doesn’t take much effort, but if you don’t, the valve can potentially get choked and cause an explosion.

Why does the relief valve overflow when discharging water?

When water temperature exceeds the limit, a water heater typically releases a lot of hot water to lower the temperature. But an overflow could also be caused by a faulty or leaking valve.

Why does my expansion tank keep filling up with water?

If there is an excess of pressure in the heater and a lack of air in the expansion tank, the water will be forced back into the expansion tank instead of the main water supply line.

How to know if your pressure relief valve is faulty?

If you notice signs like reduced pressure in the heater, high or no water pressure, or even vibrating sounds from the pipelines, chances are the valve has gone bad.

How do you fix a leaking temperature and pressure relief valve?

A T&P relief valve is a quick fix and is easily replaced by most DIYers. Just grab a new one from your local hardware store for a few bucks to make your heater new again.

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