First, Don't Panic — Most Furnace Leaks Are Water, Not Gas
Finding water pooling around the base of your furnace is alarming, but in the vast majority of cases it is a condensate or plumbing issue rather than a dangerous fault. A modern high-efficiency furnace actually produces water as a normal by-product of combustion, and most leaks trace back to that water not draining away the way it should.
That said, there is one exception you must rule out first. If you smell rotten eggs or sulphur, hear a hissing sound, or your carbon monoxide alarm is sounding, treat it as an emergency: leave the home immediately, then from outside or a neighbour's call FortisBC at 1-800-663-9911 or 911. After you are safe, call us at 604-359-1081. For everything else, read on — the cause is usually straightforward to diagnose and repair.
Furnaces in our service area are handled by our parent company, CanroHeat, who service furnaces, heat pumps, and tank and tankless water heaters alongside boilers. Same trusted team, same number: 604-359-1081.
The 5 Most Common Causes of a Leaking Furnace
1. Clogged condensate drain line. High-efficiency (condensing) furnaces create several litres of acidic water per day. That water exits through a small PVC drain line that can clog with algae, sediment, or sludge. When it backs up, water overflows from the drain trap onto the floor. This is the single most common cause we see in the Lower Mainland.
2. Cracked or full condensate pump. If your furnace sits below the drain line or in a basement, a small condensate pump lifts the water to a drain. A failed pump, a stuck float, or an unplugged unit means the reservoir overflows.
3. Plugged or dirty air filter. A filter left in too long restricts airflow, causing the evaporator coil above the furnace to freeze. When the system cycles off, that ice melts and drips down through the furnace — looking exactly like a furnace leak.
4. Condensation from an improperly sized or vented flue. A standard-efficiency furnace paired with the wrong metal vent can let exhaust cool and condense inside the flue, dripping back down into the cabinet.
5. A cracked heat exchanger (less common, more serious). A failed heat exchanger can sometimes show as moisture, and it carries a carbon monoxide risk. This is the one cause that is genuinely urgent — we cover it in detail in our cracked heat exchanger guide.
How to Tell a Condensate Leak From a Serious Problem
Clean, clear water collecting near the drain line or condensate pump is almost always a harmless condensate issue. The water is mildly acidic but poses no immediate danger to your home beyond the moisture itself.
Warning signs that point to something more serious include: a sooty or rusty residue around the burner area, a yellow or flickering burner flame instead of a steady blue one, visible cracking or corrosion on the heat exchanger, or any symptom that coincides with a carbon monoxide alarm. If you notice these, shut the furnace off at the thermostat and call CanroHeat at 604-359-1081 before running it again.
In Greater Vancouver's damp climate, we also see leaks worsen in shoulder seasons when furnaces run intermittently and condensate sits in lines longer, giving algae more time to grow. An annual fall tune-up clears those lines before heating season.
What You Can Check Safely — and What to Leave to Us
Before you call, there are a couple of safe checks. Replace your air filter if it looks grey and clogged — this alone resolves a surprising number of "leaks" caused by a frozen coil. Confirm the condensate pump (if you have one) is plugged in and that its float moves freely. Wipe up standing water so you can see whether it returns and where it originates.
What to leave to a licensed technician: clearing a clogged condensate line under pressure, replacing a condensate pump, neutralizing acidic drain water, inspecting the heat exchanger, and anything involving the gas valve or burner. These require the right tools and a Red Seal gas fitter's training.
When you call, tell us the furnace brand, roughly how old it is, whether the water is clear or discoloured, and whether it happens while heating or cooling. That helps our CanroHeat dispatcher send the right parts on the first visit.
Get It Fixed Before It Damages Your Floors
A small furnace leak rarely fixes itself, and condensate water is acidic enough to stain concrete, rot subfloor, and corrode the furnace base over time. Catching it early keeps a modest service call from turning into a furnace replacement.
CanroHeat services furnaces throughout Greater Vancouver, with same-day and weekend appointments available during heating season. Call 604-359-1081 for a diagnosis and an exact quote — no guesswork, no fabricated pricing.