Quick answer
Fixing a furnace leaking water costs $150–$350 when the cause is a clogged condensate trap or drain line, and $250–$450 for a new condensate pump. Most leak repairs fall inside the $150–$800 furnace repair range. The exception is a leaking secondary heat exchanger at $1,500–$3,000, which on an older furnace usually means pricing a replacement instead.
What it costs to fix a furnace leaking water comes down to where the water is escaping, and on a high-efficiency furnace that is usually somewhere cheap. A condensing furnace makes water every hour it runs and sends it to a drain through a trap, a few hoses and sometimes a pump. Most leaks are that drainage path backing up, not the furnace failing. The diagnostic visit is $90–$150 and is credited to the repair when you proceed.
Furnace water leak repair costs in Ontario, cheapest to dearest
- Clogged condensate trap or drain line: $150–$350. The trap fills with slime and scale, water backs up into the cabinet and spills out the bottom. This is the most common leak repair on a condensing furnace.
- Failed condensate pump: $250–$450 installed. Where the furnace sits below the drain, a small pump lifts the water; when its float sticks or its motor dies, the reservoir overflows. See condensate pump replacement.
- Split drain hose or loose clamp inside the cabinet: usually the low end of $150–$450, since the part is small and the labour is in tracing the drip.
- Cracked collector box or drain pan: a moulded plastic part at the heat exchanger outlet that warps or cracks with age. Parts are model-specific, so the price follows the diagnosis and normally stays within the $150–$800 repair range.
- Cracked inducer housing: water seeps from the seam of the draft inducer. The housing generally comes with the motor as one assembly, which puts the repair at the inducer price of $400–$900.
- Leaking secondary heat exchanger: $1,500–$3,000 in parts and labour. The coil that wrings the last heat out of the exhaust corrodes through, and water drips from the heat exchanger section itself.
If water reached the pressure switch or the control board before anyone noticed, that part is added to the bill: $250–$500 for a pressure switch, $500–$1,200 for a board. That is the case against leaving a slow drip for the rest of the season.
Leaks at the furnace that are not the furnace
A puddle at the base of the furnace does not prove the furnace made it. Three neighbours share its cabinet, its ductwork and its drain, and each one is cheaper to fix than furnace internals.
- Humidifier feed or drain: a bypass humidifier has a water line, a solenoid valve and its own drain hose. A solenoid stuck open, a pad scaled solid by hard Halton or Hamilton water, or a kinked drain sends water down the outside of the cabinet. A new pad is about $20–$40; see why a furnace humidifier leaks.
- Air conditioner coil pan: in summer the evaporator coil above the furnace drips into a pan with its own drain line. A leak that shows up in July with the heat off is the coil pan or that drain, and the furnace is only what the water lands on.
- Vent pipe sloped the wrong way: the plastic exhaust pipe has to slope back toward the furnace so condensation runs to the trap. A sagging run, or one pitched toward the outside wall, holds water that then leaks at a joint or freezes at the termination.
- Mid-efficiency furnace with a metal flue: it has no condensate system at all, so water at its base is one of the three sources above or condensation running back down the chimney, which calls for a venting inspection.
When a leaking furnace turns into a replacement conversation
Price a replacement when the secondary heat exchanger is the leak, the furnace is past about 15 years and the part is out of warranty. At $1,500–$3,000 the repair is a third to half the cost of a new furnace, spent on a machine whose inducer, board and blower are the same age. High-efficiency furnace installs run $4,500–$7,500.
Look up the warranty before deciding. Heat exchangers often carry much longer parts coverage than the other components, and a covered part reduces the job to labour. Every other leak on the cost list is a repair, whatever the age of the furnace.
Is it safe to keep running a furnace that is leaking water?
Usually for a day or two, with conditions. If the water is clear, the furnace is heating normally and a tray catches the drip, it can wait for a booked visit.
- Turn it off and call the same day if water is dripping onto the control board or wiring.
- Turn it off and call the same day if the leak is at a vent pipe joint, since that pipe carries exhaust as well as water.
- Call the same day if the furnace is locking out or the water is rusty.
- It can wait a few days if the drip is slow, clear and contained, and the furnace runs normally.
Condensate is mildly acidic. Left alone it rusts the cabinet floor, stains concrete and ruins anything cardboard stored beside the furnace, so move storage away and empty the tray daily.
The causes are explained in more depth in why a furnace leaks water. ZK Mechanical finds the source before quoting, puts the price in writing and credits the diagnostic to the repair. Book furnace repair in Burlington, Oakville, Hamilton and the surrounding area, compare typical figures on the pricing page, or contact us with a photo of where the water is showing.