Water Heater Leaking From the Base or Bottom
Water is pooling under or around the unit — on a tank heater that's often serious (a failing tank), but on a condensing tankless unit a puddle at the base can just as easily be a blocked condensate drain, which is a very different and much simpler fix.
Most likely causes, ranked
- Blocked or full condensate drain (condensing tankless models). High-efficiency condensing units produce acidic condensate that has to drain continuously; if the line or trap clogs, it backs up and drips or pools at the base. This is documented directly as Rinnai 25 — Condensate Trap Error and the condensate-drain variant of Rheem 29.
- Condensate shipping plug never removed at installation. New condensing units ship with a plug protecting the condensate port; if it's never pulled during install, the condensate has nowhere to go — also covered under Rheem 29.
- Failing tank on a storage water heater. Corrosion pinholes in an aging steel tank are a real leak with no fix except replacement — tanks don't get patched. This tends to get worse over hours or days, not come and go.
- Temperature-and-pressure (T&P) relief valve discharging. This valve is designed to open and drip if pressure or temperature inside the tank gets too high — an occasional drip after heavy use can be normal, but frequent or continuous discharge is not.
- Loose fitting, drain valve, or supply-line connection. A loose drain valve at the bottom of a tank, or a fitting that was never fully tightened, can leak steadily without the tank itself being damaged.
- Condensation from the cold-water inlet line (not the unit itself). In humid conditions, moisture beading on a cold pipe nearby can look like it's coming from the heater when it isn't.
Check this first
- With power and (for gas units) attention to safety, dry the area completely, then watch for where water first reappears — the exact source narrows the list fast.
- On a condensing tankless unit, trace the condensate line from the unit to its drain and check for a kink, a full container, or a blockage; confirm the shipping plug was removed if this is a newer install.
- Check the T&P relief valve's discharge pipe (it should run down toward the floor) for drips versus a steady stream.
- Look at the drain valve near the bottom of a tank unit and any visible fittings for looseness or corrosion.
- If it's a tank unit and the leak is coming from the tank body itself rather than a valve or fitting, treat it as a failing tank — this isn't a homeowner repair.
Which fault code are you seeing?
If a code or blink pattern is showing alongside the leak, look it up directly: code lookup, or jump to a brand: Rinnai, Navien, Rheem, AO Smith.
When to call a professional
Call a licensed plumber if the water is coming from the tank body itself (this means replacement, not repair), if clearing an accessible condensate blockage doesn't stop it, if the T&P valve is discharging continuously rather than an occasional drip, or if the leak is anywhere near electrical connections. A leaking tank on a gas unit, or water near line-voltage wiring on an electric unit, isn't something to keep monitoring — shut off the water supply to the unit if you can do so safely and get it looked at.
Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.