Lennox Furnaces and Why They Leak
Lennox is one of the more common furnace brands in Greater Vancouver homes, and many models in service here are high-efficiency condensing units — the SLP, EL, and ML series among them. Like every condensing furnace, a Lennox produces acidic condensate as a normal part of reaching its high efficiency, so the most frequent leaks trace back to the condensate drainage path rather than a brand-specific defect.
That's reassuring, because it means a leaking Lennox is usually a straightforward repair: restore proper drainage and the leak stops. The principles are the same as any high-efficiency furnace, with a few Lennox-specific details worth knowing.
Lennox furnaces in our area are serviced by our parent company, CanroHeat. One number covers Lennox furnaces, boilers, and water heaters: 604-359-1081.
Common Lennox-Specific Leak Points
Condensate trap and drain assembly. Lennox condensing furnaces route condensate through an internal trap and collection box. Over time the trap can clog with biofilm or develop a cracked fitting, weeping water at the base. This is the most common Lennox leak we see.
Inducer/collector box gasket. On some Lennox models, the gasket between the inducer assembly and the condensate collector can degrade, allowing condensate to seep. It presents as moisture around the upper furnace area rather than purely at the bottom.
Clogged drain line and pump. As with any high-efficiency furnace, the external PVC drain line and any condensate pump are frequent failure points — algae clogs and pump float failures lead the list.
Pressure switch lockouts. Lennox furnaces use pressure switches that can trip when condensate backs up, so you may see both a leak and an error condition. Many Lennox boards display diagnostic flash codes that help a technician pinpoint the fault quickly.
What You Can Check on Your Lennox Safely
A few safe checks can help before you call. Replace the air filter if it's dirty — a restricted filter can freeze a cooling coil and mimic a furnace leak. If your Lennox has an external condensate pump, confirm it's plugged in and its float moves freely. Note any flashing LED diagnostic code visible through the furnace's sight glass; Lennox encodes useful fault information there, and reading it to our dispatcher speeds diagnosis.
Wipe up standing water and watch whether it returns during heating or cooling — that tells you whether you're chasing a furnace condensate issue or an AC coil issue.
What to leave to a licensed technician: opening the Lennox cabinet, clearing the internal trap, replacing collector-box gaskets, swapping a condensate pump, and anything near the gas valve, burner, or heat exchanger. And if you ever smell gas or your CO alarm sounds, leave the home and call FortisBC at 1-800-663-9911 or 911, then CanroHeat at 604-359-1081.
Get Your Lennox Diagnosed and Fixed
A leaking Lennox furnace rarely resolves on its own, and acidic condensate left to pool will damage your floors and the furnace base. The fix is usually quick once the source is pinpointed — often a trap or drain clearing, a gasket, or a pump.
CanroHeat services Lennox furnaces throughout Greater Vancouver, reads Lennox diagnostic codes, and carries common condensate parts for one-visit repairs. Same-day and weekend availability in heating season. Call 604-359-1081 for a diagnosis and an exact quote.