Why Is My Boiler Leaking Water?

HVAC Logo IconBy HVAC.comJanuary 24, 2025
Boiler radiator

Coming home to find your boiler leaking water can quickly turn into a homeowner’s nightmare. Whether it’s a steady drip or a puddle forming beneath your boiler, the sight of water where it shouldn’t be raises immediate concerns. Is the problem minor, or could it mean costly repairs – or even a full replacement?

If you’re asking, “Why is my boiler leaking water?”, this is a common problem that can stem from a variety of causes, from high pressure to faulty components. HVAC.com explains why it happens and what steps to take to resolve the issue.

Why Is My Boiler Leaking Water from the Bottom?

If you’ve noticed water pooling beneath your boiler, it’s a clear sign that something is wrong. Here are the issues that are most often the cause of a hot water boiler leaking from the bottom:

Corroded Boiler Tank or Components

Over time, metal components within your boiler can corrode from exposure to water and oxygen. Corrosion weakens the boiler’s tank or pipes, which eventually leads to leak. If you notice rusty water when your boiler is leaking from the bottom, corrosion is likely to blame

If corrosion is limited to a specific part, replacing the component may be a repair option. However, severe corrosion throughout the system usually means it’s time for a new boiler.

Leaking Heat Exchanger

The heat exchanger heats the water in your boiler. Cracks in the heat exchanger can result in the boiler leaking from the bottom. This is more common in older systems or boilers that have been overworked. Unfortunately, a cracked heat exchanger is often expensive to repair, and, in most cases, replacing the entire boiler may be the most cost-effective solution.

Loose or Damaged Drain Valve

The drain valve is used to remove water from the boiler during boiler maintenance or repairs. If this valve is loose or damaged, you may find your boiler leaking from the bottom of the unit. In this case, tighten the valve if it’s loose. If the leak continues, the valve may need to be replaced.

Internal Component Failure

Boilers have multiple seals and joints to keep water contained within the system. These seals can deteriorate due to age, wear, and temperature fluctuations over time, causing a boiler dripping water onto the floor. You may also notice low pressure if a seal is bad. A leaking seal can usually be replaced, which is a straightforward repair for a professional technician.

Why Is My Boiler Dripping Water From a Pipe?

If you’ve noticed water dripping from one of the pipes connected to your boiler, here are the system issues that may be behind the leak:

Faulty Pressure Relief Valve

The pressure relief valve is a safety mechanism that prevents your boiler from building up dangerous levels of pressure. If the system pressure gets too high, this valve will release water to protect the boiler – this is normal. Keep an eye on the pressure gauge, as levels should go down as the valve releases pressure. If the pressure continues to climb, call a technician to inspect the system

However, if the valve is malfunctioning, water may leak from the bottom of the boiler at other times. A professional can inspect and replace the faulty valve if necessary. 

Condensation Overflow

Modern high-efficiency boilers produce condensation as they run. This condensation is normally drained away through the condensate pipe. If the pipe is clogged or damaged, condensation can back up and leak out of the boiler, which produces the water puddles you find around the bottom of the unit.

If you notice your high-efficiency boiler leaking from the bottom, check the condensation pipe for blockages. Also, make sure it’s securely connected. If damaged, a technician can replace it.

Leaking Heating System Pipes

The pipes that distribute hot water to your radiators or taps can sometimes spring leaks, which can cause the boiler to drip water from a pipe. These leaks often happen at connection points or along the length of the pipe due to loose fittings, corrosion, or wear and tear over time.

Tighten loose connections if possible, or have your HVAC technician handle this for you. If pipes are damaged or corroded, the affected sections likely need to be replaced to stop the leak.

Expansion Vessel Issues

The expansion vessel in a sealed boiler system absorbs the extra water volume created when the water heats up. If this vessel fails, it’s likely caused by a ruptured diaphragm. Rising pressure in the boiler causes leaks from the relief valve pipe or other areas of the system. A boiler technician can test the expansion vessel and either repressurize or replace it if it’s faulty.

Steps to Take When You Have a Leaking Boiler

If you’ve noticed a leak from the bottom of your boiler or a pipe, follow these steps to prevent more damage and fix the issue:

  1. Turn Off the Boiler: Shut off the system to prevent further water loss or potential damage to the internal components.
  2. Inspect the Leak: Try to identify where the water is coming from. Look for obvious signs like a boiler relief valve leaking, corroded pipes, or water pooling around the base.
  3. Check the Pressure: If the pressure gauge is too high or too low, this could provide a clue about the source of the problem.
  4. Call a Professional: While some minor issues like tightening a connection can often be handled by homeowners, most boiler repairs require hiring a technician for safety and efficiency.