Tankless Water Heater Leaking? The 5 Places Water Gets Out
A tankless water heater has no tank to rust through, so when a tankless water heater is leaking, the cause is almost always one of five specific places. Most are fixable; one is serious.
Turn the unit off at its power switch or breaker and close the cold isolation valve beneath it before you look.
1. The pressure relief valve
Tankless units have a relief valve too, often on the hot side under the unit. Like a tank's valve, it drips when it is worn or when pressure is too high.
2. The isolation or service valves
The hot and cold valves under the unit, used for flushing, can leak at their stems or caps. These are among the easiest tankless leaks to fix.
3. The condensate line
High-efficiency condensing units make acidic condensate that runs out through a small drain line. A disconnected, blocked or cracked line drips under the unit and is easy to mistake for a water leak.
4. The inlet and outlet connections
The fittings where the house pipes meet the unit can loosen or corrode, just like on a tank.
5. The heat exchanger
Water dripping from inside the cabinet can mean the heat exchanger itself is leaking, often after years of scale build-up or corrosion. That is the serious one: it may be a major repair or the end of the unit, depending on age and warranty.
Why hard water matters so much on a tankless unit
Minerals coat the narrow passages of the heat exchanger. Regular flushing through the service valves keeps it clear, and skipping it is one of the most common reasons a tankless unit fails early.
Repair cost and lifespan
Tankless leak repairs are estimated at $150 to $1,300, with valves and connections at the low end. Tankless units commonly last 15 to 20 years or more, so a leak on a younger unit is usually worth repairing. Compare it with the other common fixes, or book water heater leak repair near you.
Quick answers
Why is my tankless water heater leaking from the bottom?
Usually the relief valve, the service valves, the condensate line or a connection. Water from inside the cabinet can mean the heat exchanger.
What would cause a tankless water heater to leak?
Worn valves, loose connections, a condensate line problem, high pressure, or scale and corrosion in the heat exchanger.
What's the average lifespan of a tankless hot water heater?
Commonly 15 to 20 years or more, longer with regular flushing.
Leak still running?
A plumber who handles leaking water heaters can trace it and quote it in writing.
