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Furnace Making Running Water Noise? Common Causes and Fixes

It’s normal for furnaces to make sounds. You’re probably used to the clicks, crackles, and whooshes that occur as gas gets ignited and hot air passes through the vents. However, what could possibly be making a running water noise in your furnace?

Your furnace is making a running water noise because of a clogged condensate drain line or drain pump or an issue with the refrigerant. Fix the problem by examining and cleaning the drain line and having an HVAC technician check the refrigeration system.

This article will explain how to identify where the water sound is coming from and what’s causing it. I’ll also share a few quick fixes for each problem so that your furnace can keep your house warm for another cold season.

Identify the Location of the Noise

The running water sound can come from different places, from the furnace itself to the walls. When your furnace’s thermostat is set to heat, a pump begins to circulate hot water.

The water passes through the radiators, warms up your home, and the cold water returns to the furnace. You will hear the water running through the pipes and radiators, which is normal. The sound stops once the ducts or radiator heats up. Of course, this only applies if you have a water-based heating system.

 If the sounds emanate from the walls, your ductwork could be the issue. If you can’t trace the sound source, another heating system component could malfunction; either the water tank or baseboard.

Trace the Water Leakage

Check the drain pan; there is a possibility that it filled up and is overflowing. If the water is coming from the walls, then the problem is the condensed moisture from the ducts. When you find a leakage directly in front of the furnace and right up to the evaporator coils, it means your drain pipe is clogged.

Clogged Condensate Drain Line

Sometimes your furnace’s air handler drains with gravity instead of the drain pump. When your HVAC system heats or cools the air, it produces moisture that must be drained. The drain line expels the moisture outside your house through an exterior wall.

When you hear water noises, then it could be that the drain line is clogged. A clogged drain line will cause water damage in your home by redirecting moisture back to the furnace.

How To Fix

You can choose where to unclog your pipe from. If you clean it from outside, use a shop vacuum to clean out the clogs by placing them at the end of the drain line and locking them with duct tape to prevent air from escaping the pipe.

I recommend using the Vacmaster Wet Vacuum Cleaner ( because it’s multi-operational, lightweight, and has strong suction. Turn on the shop vacuum and let it suck debris from the pipe. It’ll only take about 10 seconds.

Vacmaster 3 Peak HP 5 Gallon Wet Dry Vacuum Cleaner Lightweight Powerful Suction Shop Vacs with Blower Function for Dog Hair,Garage,Car,Home & Workshop

This video shows how to clean a high-efficiency gas furnace’s condensate drain.

Clogged Drain Pump

When a drain pump starts to fail, water build-up will create noise as the pump pushes the water outside your house. This can even get worse and cause water leakage from your HVAC system, exposing your floor to water damage. When water sits for some time, mold will grow inside the pump and clog it.

How To Fix

  1. Check the pump for water leakage.
  2. Turn off the power supply to the drain pump at the circuit board.
  3. Locate the PVC pipe connected to the drain pan and disconnect it.
  4. Carefully remove the pump.
  5. Remove any dirt, mold, or algae from the pump using the vacuum cleaner.
  6. Clean the pump using a bleach solution; I recommend mixing water with Clorox Splash-less Bleach ( Pour the solution into the drain to disinfect the pump and kill anything growing inside it.
  7. Connect everything back in place, including the power supply.
Clorox Splash-Less Bleach, Regular, 2 Pack of 55 fl oz each/ 110 Ounces Total

If this doesn’t make the pump function correctly, it’s better to shut everything off and call a qualified HVAC technician to troubleshoot your furnace.

Issues With the Refrigerant

When your refrigerant is undercharged, you’ll hear a running water sound in the high-pressure refrigerant line. When you hear the noise in the refrigeration system suction, it could be because the liquid refrigerant has moved to where only gas refrigerant should be.

How To Fix

Overcharged refrigerants are a danger and can damage other HVAC system components. Shut off your HVAC system and contact your HVAC technician as early as possible after hearing the noise.

How To Prevent a Running Water Noise Coming From the Furnace

  • Regularly clean out the condensation tray to avoid clogging.
  • Change the air filters regularly since dirt can reach the evaporator coils and eventually travel to the drainpipe.
  • Your ducts and vents supply warm air into your rooms, and if they aren’t clean, you’re putting yourself at risk of allergies and other respiratory illnesses. Remember to clean the air grilles too.
  • To prevent water damage and constant furnace component repair and replacement, call your HVAC specialist before the winter season to perform a routine check and do minor repairs to your heating system.

Final Thoughts

Although it’s normal for furnaces to make sounds when in operation, you shouldn’t ignore the noises it makes. Furnaces should be relatively quiet.

Here’s a quick recap of the post:

  • You can diagnose your furnace quickly by locating the origin of the sound first.
  • Regular maintenance fixes minor problems before they escalate.
  • Most running water noises are related to high-efficiency furnaces.
  • When you hear a running water noise, determine whether you can see any moisture deposit on or around your furnace.
  • Call a qualified HVAC technician if you can’t figure out the problem yourself.


  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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