Furnace Leaking Water? 5 Condensate Causes (Greeley Homeowner Guide, 2026)

Greeley’s water is hard, and our winters can swing from mild to brutal in a single afternoon. Because most furnaces installed here in the last decade are high-efficiency models, they naturally produce water as they run.

Put those three facts together, and it’s no surprise that a furnace leaking water onto the basement or utility closet floor is one of the most common calls McCormick Heating & Cooling gets between October and February.

The good news is that a furnace leaking water almost never means the furnace itself is failing. In most Greeley homes, it means condensate, the water byproduct of a high-efficiency furnace, isn’t draining the way it’s supposed to.

Below are the five most common causes, in the order our technicians check them, and the signs that tell you which one you’re dealing with.

Why Is Your High-Efficiency Furnace Making Water At All?

Furnaces rated 90% AFUE or higher cool their exhaust gas enough during combustion that it condenses into liquid water, like steam fogging a cold window. This is normal and expected.

The water has to go somewhere, and that “somewhere” is a small system of parts most homeowners never think about until it fails.

A typical high-efficiency furnace condensate system includes:

• An inducer motor that pulls combustion gas through the heat exchanger.
• A drain trap that collects the condensate before it exits the unit.
• The plastic drainage piping that directs excess water away from the unit and toward a sump, floor drain, or pump system.
• A float switch that shuts the furnace down if that water backs up.
• On many installs, a drain pan underneath the unit serves as a last line of defense.

If any part in that chain gets blocked, cracked, or frozen, water finds the path of least resistance, usually straight down onto your floor.

The 5 Most Common Reasons a Furnace Leaks Water in Greeley Homes

1. Blockages in the Condensate Pipe

Over a heating season, a thin layer of algae, sediment, and mineral scale builds up inside the PVC line. A furnace drain line clogged with this buildup backs water up until it overflows at the trap or the furnace cabinet itself.

2. A Dry or Blocked Condensate Trap

The trap is designed to hold a small amount of water as a seal. If it dries out over the summer or gets clogged with debris, water bypasses it and leaks at the connection point instead of flowing through.

3. A Broken or Overflowing Condensate Basin 

Plastic drain pans become brittle with age and heat cycling. A hairline crack lets water escape slowly, often pooling on the floor only after the furnace has been running for a while.

4. A Failed or Sagging Drain Line Pitch

For proper gravity drainage, PVC piping needs a gentle downward slope. When a pipe droops, moves out of place, or lacks adequate tilt from the start, moisture collects in the dips and eventually overflows back into the heating system.

5. A Tripped or Stuck Float Switch

This safety switch should shut the furnace off before water overflows. When it sticks in the “open” position, water keeps draining normally. When it fails stuck “closed,” the furnace won’t start at all, which is a different symptom with the exact same root cause.

Not sure if your furnace is actually leaking water or if it’s an ignition problem that just looks similar?

The Fort Collins Homeowner’s Guide to a Furnace That Won’t Start walks through how a stuck float switch can shut heat off completely, with no visible water at all, which is one reason the two problems get confused.

McCormick Heating & Cooling has worked on condensate systems across Greeley, Loveland, and Fort Lupton for two decades, so this list reflects what we actually see on service calls, not a generic troubleshooting checklist.

If you’re already past the point of guessing, a technician visit typically runs one to three hours and ends with you looking at the exact failed part before anything gets replaced.

Contact us today to schedule a diagnostic visit.

Furnace Leaking Water When the Heat Is On? Here’s What That Signals

Timing matters more than most homeowners realize. If you only notice moisture while the heating cycle is running and never when it is resting, the issue is typically the drainage piping or the trap, not a damaged catch pan.

• Leaking only during the first few minutes of a heating cycle: often a dry trap or a line that’s just starting to back up.
• Leaking that gets worse the longer the furnace runs: usually a partial clog that a full flow can’t push past.
• Steady dripping even hours after the furnace shuts off: points to a cracked drain pan or a line with standing water.
• Water appearing only during a hard cold snap: suggests a frozen section of line rather than a clog.

Clearing a clogged drain line or replacing a cracked trap is typically a straightforward same-visit repair.

A full drain pan replacement or float switch swap takes a bit longer since the technician needs to access the furnace cabinet, but neither is a major-component repair in the same category as a cracked heat exchanger.

Furnace Condensate Leak vs. Furnace Won’t Start: Same Root Cause, Different Symptom

A furnace condensate leak and a furnace that refuses to start are often two symptoms of the exact same blockage, just caught at different stages. Early on, water backs up slowly enough to overflow visibly before the float switch reacts.

Left alone, the backup eventually reaches the switch, which does its job and shuts the system down to prevent water from reaching electrical components.

This is why a homeowner who ignores a small drip for a few weeks sometimes wakes up to no heat at all during the next cold stretch, with the furnace showing no obvious water on the floor anymore because the switch finally caught it.

Why Greeley’s Water and Winters Make Condensate Problems Worse

Greeley’s conditions aren’t identical to the rest of the Front Range, and that affects how often condensate systems fail here specifically.

• Hard water: Greeley’s municipal water commonly tests in the 10 to 11 grains-per-gallon range, which accelerates mineral scale buildup inside condensate lines and traps compared to softer-water areas
• Freeze-thaw cycling: winter temperature swings of 30 or more degrees within a day stress PVC fittings and joints, which can crack or loosen over several seasons
• Longer cold stretches: sustained hard freezes during a Weld County cold snap are long enough to freeze an exterior-routed condensate line solid, especially on older installs
• Rapid adoption of high-efficiency furnaces: as more Greeley homes replace older 80% AFUE units with 90%+ models, more households are dealing with condensate systems for the first time

A homeowner in west Greeley called McCormick last winter after noticing water pooling near the furnace base every afternoon. The furnace itself was running fine, no lockouts, no error codes.

The cause turned out to be mineral scale narrowing the drain line enough that it could only keep up with slow drips, not a full condensate flow. A line flush and trap cleaning solved it in under an hour.

DIY Checks vs. When to Call a Greeley Furnace Technician

A few checks are safe to try before calling for service:

1. Grab a flashlight to look for external cracks along the pipe and pan without removing any hardware.
2. Look at the drain line exit point to confirm water is actually flowing out when the furnace runs.
3. Check for ice buildup on any exterior-routed section of line during a cold snap.
4. Reset the float switch only if your furnace manual shows exactly where it is and how.

Call a professional technician right away if you find moisture gathering directly inside the heating cabinet, discover ice forming on the drain tube, or find yourself repeatedly pressing the float switch reset.

Repeated resets without finding the actual blockage usually mean the problem is further down the line than a homeowner can safely reach.

For anything beyond a visual check, Furnace Repair from a NATE-certified technician covers a full inspection of the drain system, trap, float switch, and drain pan in a single visit, with the failed part shown to you before any repair happens.

McCormick Heating & Cooling has been headquartered in Greeley for over 20 years, backed by more than 1,100 verified 5.0-star Google reviews. You can see our current reviews and service details on our Google Business Profile.

Key Takeaways

• When water pools around your heating unit, it usually points to a backed-up condensate drain rather than a broken furnace.
• Timing matters: leaks only during a heat cycle usually point to the drain line or trap, while leaks after shutdown often mean a cracked drain pan.
• Greeley’s hard water and sharp winter temperature swings make scale buildup and frozen lines more common here than in milder climates.
• A clogged drain line or dry trap is often a quick, same-visit fix once a technician confirms the actual blockage point.

Don’t Let a Small Drip Turn Into a No-Heat Call

Water around your furnace is annoying, but it’s rarely dangerous on its own. The real risk is waiting long enough that the same blockage trips the float switch and leaves you without heat during the next cold snap.

Catching a condensate issue early, while it’s still just a drip, is almost always the cheaper and faster fix.

If you’ve spotted water near your furnace this season, don’t wait to see if it clears up on its own. Reach out to McCormick Heating & Cooling today and get the exact cause diagnosed before a small leak becomes a bigger repair.

Frequently Asked Questions

What makes a heating system leak water?

A furnace leaks water most often because condensate from a high-efficiency unit isn’t draining properly, usually resulting in standing water on your floor.

This points to a fully clogged main drain line, a completely blocked trap, or a frozen section of PVC line during extreme cold weather. In older, non-condensing furnaces, a large leak can also come from a broken humidifier connection.

Why is my furnace dripping water?

Unlike a major leak, a slow, steady drip usually means water is still draining, but the system can’t keep up with the volume. This typically points to a partial clog where mineral scale has narrowed the pipe, an improperly pitched drain line, or a hairline crack in the drain pan.

Dripping that worsens the longer the furnace runs confirms the blockage is still letting some water through, just not enough.

Why is my furnace leaking water when the AC is on?

Furnaces and central air conditioners often share the same condensate drain line and drain pan, so a clog or crack affecting one system shows up as a leak when either the furnace or the AC runs.

If water only appears during cooling season, the blockage is likely in the shared line rather than furnace-specific components, and the fix is the same drain cleaning or trap repair either way.