Rinnai Dripping at the Exhaust After Shutoff
On this page (5 sections)
The Short Answer: A little water at a Rinnai’s exhaust after the burner stops is usually condensation from the vent pipe or rain entering the terminal. It becomes a concern when water keeps coming with the heater off, when the condensate drain is blocked, or when the volume is large and steady, which can mean a leaking heat exchanger. Never seal or caulk a vent to stop drips.
Where vent water comes from
Hot exhaust carries water vapor. When it meets a cooler vent pipe, some condenses and runs back toward the heater or out of the terminal. That happens on both types of Rinnai:
- Condensing models (SENSEI and other high-efficiency units) are designed to condense water and send it out through an internal trap and a drain line.
- Non-condensing models still get some condensation in the vent. Rinnai’s professional troubleshooting guide (opens in a new tab) calls for a condensate drain trap at the vent connection on top of non-condensing indoor units, and lists a missing or clogged trap among causes of ignition and flame problems.
After the burner stops, the fan runs briefly, and water left in the vent can drip out at either end.
Sorting it out
| What you see | Most likely | Urgency |
|---|---|---|
| A few drops at an outdoor terminal after long use, then dry | Normal vent condensation | None |
| Drips only after wind-driven rain | Rain entering the terminal | Low; ask about cap or terminal position |
| Steady drip at the vent connection on top of an indoor unit | Condensate trap at the vent missing or clogged | Service soon |
| Condensing model, drain line kinked, frozen, or full pump, and water at the vent or cabinet | Condensate backing up; may show code 10 or 25 | Fix the drain path |
| Water keeps coming with the heater off for hours | Possible heat exchanger leak | Turn off and call |
A safe test you can do
Close the cold-water valve feeding the heater and turn the heater off. If dripping slows and stops within a short time, it was vent condensation draining out. If a steady flow continues, or resumes only when you reopen the water valve, water is getting from the plumbing side into the combustion side. Rinnai’s guide names liquid coming out of the condensate drain while the heater is not operating as a common sign of a leaking heat exchanger.
Also check the drain path on condensing units: the condensate line should run downhill to a drain or working pump, without kinks or ice.
What the technician checks
A technician inspects the vent for correct slope, joints, and approved materials, confirms the condensate traps (internal and, on non-condensing indoor units, at the vent connection), and looks for moisture inside the combustion chamber, on the burner, and in the gas-valve tubing. If the heat exchanger is leaking, it must be replaced; on older units that often leads to replacing the heater. A missing vent trap or blocked drain is a minor repair.
Do not run a heater that is putting water into the burner area, and do not seal the vent with caulk or tape: a sealed or blocked vent can push exhaust indoors.
Related: Rinnai code 25 condensate faults, water dripping from a water heater exhaust, and a frozen Rinnai.
Frequently Asked Questions
Q: Is the water from a Rinnai vent safe to touch? A: Vent condensate is mildly acidic. Brief contact is not dangerous, but rinse it off, and do not let it drip onto finishes or plants long term. A drain or neutralizer solves repeated dripping.
Q: Could the drip be the pressure relief valve? A: The relief valve is on the water connections and discharges through its own pipe, not through the vent. If its discharge line is wet, see Rinnai pressure relief valve leaking.
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.
- Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (opens in a new tab)Rinnai SENSEI and non-SENSEI models: vent condensate drain traps on non-condensing units and heat exchanger leak indicators; professional procedure.
- Rinnai: official document library (opens in a new tab)Select your exact model and owner manual before interpreting a fault or reset procedure.
- 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.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
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