Why is My Furnace Leaking Water and How To Fix It

Finding your furnace leaking water is enough to send shivers down your spine, especially when you're relying on it to keep your home warm. Unfortunately, leaky furnaces are a surprisingly common issue, and while it's definitely a cause for concern, it doesn't always spell disaster. What should I do? Do I need to call an HVAC professional? Why did my furnace suddenly leak? We understand that you have these questions and many more.

In this guide, we'll share the common reasons why your furnace is leaking water. We'll then walk you through the steps to diagnose the problem, including when it's time to call a furnace professional, and offer practical solutions to get your furnace back to its dry, efficient self. Let’s start!

Why Is Your Furnace Leaking Water? Common Causes

Before looking for a way to fix a furnace leaking water, it’s important to determine what’s really causing the problem. Because this way, you will be able to address the root cause of the issue, thus providing a more permanent and effective solution. 

• Condensation – If you have a high-efficiency furnace, condensation is a natural byproduct. However, if the condensation isn't draining properly, it can lead to leaks. It may be caused by a clogged condensate drain line, a malfunctioning condensate pump, or a cracked condensation trap.
• Clogged Air Filter – A dirty air filter can actually restrict airflow, which causes your furnace to work harder and leads to excess condensation buildup. This extra moisture can overflow from the condensate pan and result in a leak.
• Cracked Heat Exchanger – A heat exchanger is a crucial component that transfers heat from the gas burner to the air circulating in your home. If it cracks, it can leak water or even dangerous gasses like carbon monoxide.  This is a serious problem that requires immediate professional attention.
• Other Issues – Other potential causes include a clogged secondary heat exchanger, a malfunctioning humidifier (if you have one), or a leak in the plumbing connected to your air conditioner (if it shares the same drain line).

How to Fix Furnace Leaking Water



Fixing a furnace leaking water can be a DIY project, but it’s always recommended to consult an HVAC professional first before doing so – especially if you don’t have any knowledge about fixing or troubleshooting furnaces. Nevertheless, if you’re planning to fix your furnace leak, here’s how to get started:

1.Locate the Leak

Examine the area around the furnace for any visible signs of water. Trace the path of the water back to its origin, noting the specific component or pipe it seems to be coming from. Observe when the leak occurs – only during heating, cooling, or continuously – as this information can help diagnose the issue.

2. Power Down

Prioritize safety by turning off the furnace at the thermostat and circuit breaker. If your furnace has a humidifier, shut off its water supply as well. This will prevent the leak from worsening and eliminate any electrical hazards.

3. Inspect the Pump

High-efficiency furnaces often utilize a condensate pump to remove excess water. Ensure the pump is plugged in and listen for a humming sound, indicating it's functioning. Check the drain line for any kinks or blockages, clearing them if necessary. If the pump appears operational but isn't pumping water, examine the float switch to ensure it's not stuck. If the pump remains unresponsive, replacement may be required.

4. Examine the Drain Lines

These lines carry water away from the furnace and pump. Inspect them thoroughly for cracks, holes, or loose connections where water could be escaping. Use a pipe cleaner or similar tool to clear any debris or buildup that may be obstructing the flow. Verify that the drain line slopes downwards to allow for proper drainage.

5. Check the Humidifier

If your furnace has a humidifier, it could be the source of the leak. Start by inspecting the drain pan for any cracks or overflows, emptying or replacing it if necessary. Examine the humidifier filter for dirt or clogs, as these can lead to overflow and leaks. Ensure the water supply line to the humidifier is properly connected and not leaking.

6. Investigate Other Possibilities

If the leak isn't attributed to the condensate pump, drain lines, or humidifier, consider other potential causes. In systems with combined heating and cooling, check the air conditioner's condensate drain line for any issues. If you suspect a cracked heat exchanger in the furnace, turn it off immediately and contact a qualified HVAC technician due to the potential dangers. Other possibilities include a clogged air filter, issues with a secondary heat exchanger, or problems with the inducer motor or pressure switch.