Rheem Tankless Leaking Inside the Cabinet
On this page (5 sections)
The Short Answer: Water in or under a Rheem tankless doesn’t always mean the heat exchanger has failed. It may come from a loose service valve or inlet filter cap, the pressure relief valve, condensate on condensing models, or rain getting into an outdoor unit. If water is dripping onto the electronics or burner, turn the unit off at the power switch, close the water valves, and call a technician.
Find out where it’s coming from
Start from the outside without removing the cover. Dry everything you can reach, run a hot faucet for a minute, then look again.
| Where the water appears | Likely source | Urgency |
|---|---|---|
| At the service valves or pipe connections under the unit | Loose union or valve packing | Low to moderate |
| At the cold inlet filter cap | Filter cap not seated, or a worn O-ring after cleaning | Low |
| From the relief valve or its discharge pipe | High water pressure, thermal expansion, or a worn valve | Moderate; never cap it |
| From a plastic drain line, cool, only while the burner runs (condensing models) | Condensate drain blocked, disconnected, or frozen | Moderate |
| After heavy rain, outdoor unit only | Water entering through the vent or cabinet | Moderate; check after it dries |
| After a freeze, then a thaw | Split heat exchanger or internal pipe | High; shut it off |
| Dripping from inside the cabinet with all external connections dry | Heat exchanger or an internal water component | High; shut it off |
Rheem’s non-condensing RTG models aren’t designed to drain condensate through the cabinet. Water inside one of those is usually supply water, rain, or freeze damage. Condensing models do produce condensate, which must drain freely. See Rheem tankless water heater troubleshooting for which type you have.
What you can check safely
- Isolate the leak. Close the cold-water service valve to the heater. If dripping slows and stops as pressure falls, it is coming from the water side.
- Check the inlet filter cap if the leak started after cleaning the filter. A cap that isn’t fully seated or a pinched O-ring is a common cause.
- Look at the relief valve discharge pipe. If it drips during or after heating, the cause may be high house pressure or a failed expansion tank. See water heater expansion tank full of water.
- Follow the condensate line on condensing models to make sure it drains downhill and isn’t kinked or frozen.
- Note the timing: after rain, after a freeze, only while running, or constantly.
What the technician will check
With power, gas, and water off, a technician removes the cover and traces water to its source: internal fittings and O-rings, the water flow sensor housing, the heat exchanger, or the condensate trap and collector on condensing models. They check whether electrical components got wet and test them before restarting. For relief valve discharge they measure house water pressure and check the expansion tank.
Repair or replace
Valves, O-rings, filter caps, condensate parts, and relief valves are routine repairs. A leaking heat exchanger, often from a freeze or long-term scale, means replacing the exchanger or the unit; ask for a quote on both. Freeze damage is generally not covered by warranty, so if your unit is outdoors, use the freeze protection the manual describes.
Related: tankless water heater leaking after freeze and tankless water heater leaking from bottom.
Frequently Asked Questions
Q: Can I keep using a Rheem tankless that drips inside? A: Not if water is reaching the electronics, fan, or burner, or the heat exchanger is leaking. A small leak at an external valve can usually wait for service with the water valve closed.
Q: The leak started right after I cleaned the inlet filter. What happened? A: The filter cap is probably not seated correctly or its O-ring is pinched or damaged. With the water off, check that the cap is fully threaded and the O-ring is in place, and replace the O-ring if it’s damaged.
Q: Is a leaking heat exchanger repairable? A: The exchanger can sometimes be replaced as a part, but on an older unit the cost can approach a new heater. Get both prices before deciding.
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.
- Rheem: owner help and support (opens in a new tab)Identify the applicable model instructions or contact Rheem support.
- 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.
- A. O. Smith technical bulletin 45: thermal expansion (opens in a new tab)Background on pressure rise in a closed water system. Pressure testing and repairs are professional work.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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