Takagi Tankless Leaking: Find the Source
On this page (6 sections)
The Short Answer: Water near a Takagi tankless usually comes from one of four places: the condensate drain on condensing models, the pressure relief valve on the hot outlet, a fitting or isolation valve, or the heat exchanger inside the cabinet. Dry everything, run hot water, and watch where it reappears. Condensate and fitting leaks are usually minor repairs; water from inside the cabinet needs a technician.
Condensing or non-condensing?
Condensing Takagi models (such as the T-H3 family) produce acidic condensate whenever they fire and have a condensate drain line, often with a neutralizer. Non-condensing models (such as the T-KJr3) do not produce a steady stream of condensate. Check the model on the rating plate. A drip from a non-condensing model’s cabinet is more likely to be supply water, rain, or freeze damage.
Match the leak
| Where and when | Likely source | Urgency |
|---|---|---|
| From the condensate drain or its tubing, only while the heater fires | Condensate line loose, cracked, clogged, or overflowing | Fix soon; acidic water can damage floors |
| From the relief valve’s discharge pipe | Pressure or temperature event, thermal expansion, or a worn valve | Do not cap; see below |
| At an isolation valve, drain cap, or the cold-inlet filter cap under the heater | Loose cap or worn O-ring | Minor repair |
| From inside the cabinet with all external fittings dry | Internal water fitting or heat exchanger | Turn off; call a technician |
| Only after rain on an outdoor unit | Water entering through the vent area or a missing cover | Inspect the installation |
| After a hard freeze or power outage in cold weather | Freeze-split water passages | Turn off; call; see leaking after a freeze |
What you can check safely
- Turn the heater off if water is near the cabinet or electrical outlet.
- Dry and watch. Wipe the fittings, the bottom of the cabinet, the condensate line, and the relief valve pipe. Open a hot tap for a few minutes, then look again. Note whether the water appears only while the burner runs.
- Feel the temperature carefully. Condensate is warm at most. Hot water from the relief valve or a supply leak can scald.
- Condensate path. Check that the drain tube is connected, slopes down, is not kinked, and that any condensate pump runs. A clogged neutralizer can back up into the heater.
- Isolation valve caps. The service ports on isolation valves have caps; make sure they are on and hand-tight.
The relief valve
Tankless installations have a pressure relief valve on or near the hot outlet. If it drips, the cause may be high household water pressure, thermal expansion in a closed system, or debris on the valve’s seat after someone tested it. A relief valve that streams, or drips constantly, needs attention from a plumber. Never plug or cap it.
What the technician will check
With the gas and power off, a technician will remove the cover and look for water at internal connections, the flow sensor, the water valves, and the heat exchanger. They will check for mineral trails that show a slow leak’s path. They will also check household water pressure and expansion control if the relief valve was the source.
Repair or replace:
- Condensate tubing, neutralizer, drain caps, and O-rings: minor repairs.
- Internal water fittings or valves: moderate repairs.
- A leaking heat exchanger: a major repair; on an older unit, replacement is often more sensible. A wet circuit board may also need replacing.
For tankless leaks in general, see tankless water heater leaking from the bottom. Other Takagi issues are on Takagi tankless problems.
Frequently Asked Questions
Q: Is it normal for water to drip from my Takagi? A: On a condensing model, condensate flowing through the drain line is normal. Water on the floor, on the cabinet, or from the relief valve is not.
Q: Can I keep using it with a small drip? A: If the drip is from an external cap or the condensate line, and nothing near the electrical parts is wet, you can usually use it briefly while arranging a repair. If water comes from inside the cabinet, turn it off.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith technical bulletin 51: puddles around a heater (opens in a new tab)Common water-leak sources and the distinction between fittings and a failed tank.
- A. O. Smith technical bulletin 15: condensation (opens in a new tab)Why combustion condensate can resemble a tank leak; not a diagnosis of another manufacturer’s model.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
Editorial standards and corrections · Prepare a useful service request