Why a Water Heater Leaks from the Overflow Pipe (Explained)

When you buy a water heater, you expect efficiency at all times. Unfortunately, those expectations won’t always be met. The best equipment breaks down or may have technical issues beyond your control. Water heaters, over time, develop internal problems that manifest themselves as overflow. Fortunately, it’s fixable. 

A water heater T&P valve discharge pipe is sometimes referred to as an overflow pipe.

If your water heater’s overflow pipe is leaking, you likely have an issue with pressure inside the tank. When the pressure in your water heater gets too high, the pressure release valve opens and expels water from the overflow pipe. A leaking overflow pipe can indicate that:

  • The temperature setting on your water heater is too high
  • There is an issue inside your tank causing pressure to increase beyond the T&P valves threshold
  • The T&P valve is not “set” properly allowign the valve to remain partially open
  • The T&P valve is faulty
  • You do not have an thermal expansion tank installed

We’ll help you understand why your heater is leaking from the overflow pipe and the steps you can take to reduce such incidents. 

Is a Leaking Overflow Pipe an Emergency?

A leaking overflow pipe, may not be an emergency. At least not in most cases. However, it can be an emergency if your water heater leaks hot water at a high rate or continuously. 

For starters, it can harm you. Water heaters typically have hot water in them. It might be an emergency if you find your place flooded from an overflow pipe leak. Not only that, but the hot water can also scald you. Even at the recommended setting of 120 degrees, hot water can leave you with severe burns. 

In such cases, your best bet would be to call a professional plumbing service. Still, you can attempt it f you have the safety equipment to stop the leak while avoiding injury. 

Why Is Hot Water Coming Out of My Overflow Pipe?

Every heater has a temperate and pressure relief valve. It has one function, as the name suggests. It relieves pressure and temperature from the heater. 

Most heaters have the pressure set at 150 pounds per square inch and temperature at either 120 degrees or 140 degrees. The T&P valve opens when the water heater exceeds these conditions. 

The overflow pipe is responsible for passing the water when the valve opens. A leak from the overflow pipe means your water heater is operating above set temperature and pressure. It needs immediate attention. 

What Causes Too Much Pressure In Hot Water Heater?

One of the leading causes of excess pressure in a water heater is when the temperature is set too high.

Manufacturers set a default temperature of 140 degrees Fahrenheit. Users lower it to 120 degrees Fahrenheit. It’s a comfortable setting for most people, and it gives you wiggle room to keep it from rising too high to uncontrollable levels. The Department of Energy advises that you lower it to 120 degrees. 

Personal safety is one of the key reasons the DOE puts out such a recommendation. At 140 degrees, there is a looming risk of scalding. Any outlet where the water comes out at such a high temperature is a potential risk. 

Beyond safety, energy saving is a great reason to adjust it to 120 degrees. According to the calculations by the DOE, you lose up to $60 annually in standby heat losses and $400 in demand losses. Bottom line, keep the temperature at 120, and you’ll have fewer leaks. 

Pressure can also come from inbound water pressure. Water systems that feed the cold water inlet sometimes have different pressure settings. The recommended water pressure should be about 80 PSI per code. Some heaters have pressure as high as 100 PSI. 100 PSI is too high and might cause huge damage to the heater, especially if the pressure stays consistent. 

When water comes in pressure as high as 100 PSI, it is subjected to high temperature. Increased temperature increases the pressure, causing it to either drain or start damaging the heater. 

If the water pressure cannot be changed, you should consider getting a pressure-reducing valve. Also, you need to have a pressure gauge handy always to check the pressure. Put in the pressure gauge at the hose bib, and it’ll tell you the operating pressure. 

How Do You Fix an Overflowing Water Heater?

1. Shut Off the Power and/or Gas

The area below the water heater should not be flooded with water if the overflow is not severe. If there is water in the area, the water heater likely has no water, and you need to shut off the gas and/or electrical supply immediately. 

2. Inspect the Heater for Leaks

Look for any leaks around the valves. If there’s a leak and the heater is off, release the pressure from the heater by flipping the T&P valve. However, flip it slowly. Most are susceptible to damage if you flip it too quickly. A leak means you may have to re-thread the valve with Teflon/plumber tape. 

3. Remove Any Debris From the Valve

Usually, dirt clogs the main seal. Find out if there is debris blocking the seal by opening and closing the valve a few times. Water should drip from the overflow pipe. Flushing should clear any dirt around the seal. 

Checking the seal to the valve is a vital step in troubleshooting the problem. 

4. Release the Pressure From the Entire System

Open a hot water faucet to remove the pressure from the heater. Since the cold water inlet is closed, it should be a momentary flow. 

Now, open the overflow at the bottom of the heater. Attach a garden hose that directs water out of the house or to your home’s drainage. Leave the overflow open for one minute. 

5. Replace the Overflow Pipe

Depending on how it was put in, you may have to cut off the overflow pipe. After removing the overflow pipe, remove the old valve and install a new one that’s sediment-free. Reattach the overflow pipe, making sure to wrap Teflon tape along the thread. 

6. Confirm All Your Fittings

Run a final check on the tightness of your valves. Reopen the cold water inlet and check the overflow pipe. If there is any leakage, you should call a plumber. 

7. Close Any Open Taps

Close the open taps that should have released all the air and pressure by now. Let the heater fill with water. Close the cold water inlet. 

8. Power On the Heater

Resume normal heater operations by powering on the heater from the main breaker. Make sure the heater fills with water before you turn on the gas or power. 

What Are the Signs of a Water Heater Going Bad?

Did you know you can prevent any heater mishaps through maintenance? Heaters rarely go out of commission without warning. Look out for these signs to figure out what you need to fix. 

  • Constant leaks – Constant leaks are a glaring sign if your water heater having structural or mechanical problems. It could be leaking from the valves or from the tank. As soon as you notice leaks from multiple places, there is a deeper problem you need to address. Fortunately, most leaks are fixable with proper maintenance. 
  •  Less hot water – Are you running out of hot water much faster than before? It could be a sign of extreme sediment buildup. See, when sediment builds up in the water heater for an extended period, it reduces water space. You might even have fine crumbs of sediment coming out of hot water outlets. You need to flush your heater. 
  • Inconsistent water temperature – Inconsistent water temperature may be a problem with tankless water heaters. It means the flow rate from the source is too low, or the heater can’t heat the water fast enough. However, where the heater has a tank, inconsistent water temperature is a sign of breaking water heating elements or a bad thermostat. 
  • Brown or discolored water – If you notice discolored water or brownish coloring in your water, there are chances your water heater has bad anode rods, and the tank is rusting from inside. Water impurities typically gravitate towards the sacrificial anode rod. If the anode rod is not replaced when it’s deteriorated, the harsh minerals in the water begin to eat away at the tank’s inner steel lining. 
  • Unusual noises – Weird noises signal a myriad of possible problems. You’d have to take a deeper look to find out the main problem. Your water heater could be overwhelmed by mineral deposits clogging valves. It might also mean your water pressure is fluctuating. The worst eventuality would be your water heater is breaking from the inside, and you need to replace it. 
  • Inconsistent water pressure from the outflows – Low water pressure is worsened by the deterioration of the heater’s inner systems. Sediment builds up fast, continually clogging systems and messing with the pressure mechanism. If you are getting low flows despite the pressure from the main water supply staying constant, check your heater. It may be about to break down and in need of repairs. 


Having a water heater comes with the additional responsibility of routine checks. Regularly checking the pressure and temperature in your system is the line between a few DIY repairs and costly replacements. The best part is, you don’t have to do the dirty work. A home inspector is well within their expertise to check your system for you and give you professional advice on what to do. 


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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
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