Most leaks on a Takagi tankless unit come from a fitting, valve, or condensate line rather than the heat exchanger itself.
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Quick answer
A leak from a Takagi tankless water heater most commonly comes from a loose or aging fitting, a discharging relief valve, a condensate drain issue on condensing models, or a failed internal seal, rather than a crack in the main heat exchanger, which is less common but more serious when it does occur. Turning off the water and power supply to the unit and calling a licensed technician promptly limits water damage and gets the actual source identified.
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If you notice water pooling near the unit, the first safe step is to shut off the cold water supply valve feeding the unit and, if you are comfortable doing so, switch off the electrical power at the breaker or unit switch. This does not require touching any gas fitting. Try to note where the water actually appears to be coming from: a fitting or connection point, the bottom of the unit itself, or a drain line, since that observation helps the technician move faster on arrival. Do not attempt to tighten fittings on a pressurized system or open any part of the unit's gas or combustion assembly yourself.
If the leak is minor and slow, it is reasonable to place a container to catch drips while waiting for service. If it is significant, shutting off the water supply is the priority.
| Step | What It Determines |
|---|---|
| Inspect all external fittings, unions, and valves under pressure | Rules out the most common and simplest leak source |
| Check the relief valve for proper seating and discharge behaviour | Confirms whether it is a pressure issue rather than a valve failure |
| Inspect the condensate drain path on condensing models | Identifies blockage or corrosion from acidic condensate |
| Pressure-test internal seals and gaskets where accessible | Locates an internal seal failure if external sources are ruled out |
| Inspect the heat exchanger itself if other sources are ruled out | Confirms whether a more serious internal failure is present |
Condensing tankless units produce acidic condensate as a normal part of their operation, and that condensate needs a properly sloped, unobstructed drain path to a suitable disposal point. Metro Vancouver's damp coastal climate and the amount of hot water use in many households mean condensate lines see steady use, and CANRO commonly finds a blocked, poorly sloped, or corroded condensate line as the actual source of what a homeowner assumed was a heat exchanger leak. This is a straightforward fix once identified, but it does need a technician to trace the drain path correctly, particularly in tighter mechanical closets common in condo and townhouse installations.
Takagi documents general condensate and fitting specifications for its condensing models, but exact drain routing and slope requirements depend on the specific installation, so this should be verified on site rather than assumed from general literature.
The large majority of leaks on a tankless unit are fittings, valves, or condensate issues that are repaired without replacing the appliance. A confirmed crack or corrosion failure in the heat exchanger itself is a different situation, and given the heat exchanger is the core component of the unit, that kind of failure generally points toward replacement rather than repair, especially on an older unit. A technician's inspection is what determines which category your leak falls into, so it is worth getting that diagnosis before assuming the worst.
Safety note
If you ever smell natural gas near the unit or anywhere in the home, leave the home immediately and call FortisBC at 1-800-663-9911 from outside. Do not attempt to relight a pilot, reset an ignition lockout, or open any gas fitting yourself. Gas connections, venting, and combustion-air work on a tankless water heater must be handled by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870.
Not on its own, unless you also smell gas, in which case leave the home and call FortisBC immediately. A water leak alone should still be addressed promptly to avoid water damage and identify the cause.
It's best not to attempt this on a pressurized water heater connection yourself; shut off the water supply instead and have a licensed technician diagnose and repair the actual source.
Condensing units produce acidic condensate as part of normal operation, and if the drain line is blocked, poorly sloped, or corroded, that condensate can back up and appear as a leak.
No, most leaks come from fittings, valves, or condensate lines and are repairable. A confirmed heat exchanger crack is less common and more likely to point toward replacement.
Yes, shutting off the cold water supply and, if comfortable, the electrical power is a reasonable first step while waiting for a technician.
Tighter mechanical closets and longer or more constrained drain runs common in condo and townhouse installs can make proper condensate slope and routing more challenging to get right.
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