E027
Navien Tankless Water Heater
Severity: CriticalWhat it means
Navien E027 means the leak-detection sensor in the bottom of the unit found water sitting in the base pan.
On NPE-2 and NPN models that sensor exists specifically to catch a heat-exchanger or fitting leak early — so treat E027 as 'find the leak,' not 'clear the code.'
Sometimes it's harmless (a condensate drip, a sweating pipe), but sometimes it's the start of a heat-exchanger failure.
Don't just reset and walk away.
Affected Models
- Navien NPE-180A2, NPE-210A2, NPE-240A2 (NPE-2 series with leak detection)
- Navien NPN-180E, NPN-210E, NPN-240E
- Navien NCB-E combi units with the leak sensor option
- Other Navien models fitted with the base leak-detection sensor
Common Causes
- Condensate hose disconnected, kinked, or its trap overflowing into the base
- Loose or weeping water connection at the inlet, outlet, or pressure-relief fittings
- Pressure-relief valve dripping
- Heat-exchanger pinhole leak (the reason the sensor exists)
- Condensation from a cold inlet pipe in a humid space dripping onto the pan
- Leak sensor itself faulty or its connector wet (rare)
How to Fix It
-
Shut off the water and look inside.
Close the cold isolation valve to the unit.
Power it off.
Open the front cover and look in the base pan with a flashlight.
Is there standing water? Is anything actively dripping? Where is it coming from — a fitting, the condensate area, or the heat exchanger? -
Check the condensate drain first.
A clogged or disconnected condensate trap is the most common harmless cause.
The acidic condensate is supposed to run out a hose to a drain — if the trap is plugged or the hose popped off, it pools in the base.
Flush the trap, reconnect the hose, route it downhill to a drain. -
Tighten and inspect every water fitting.
Dry the base completely.
Turn the water back on and watch the inlet, outlet, isolation valves, and pressure-relief connections for a bead of water forming.
Snug any loose fitting; replace a dripping pressure-relief valve. -
Watch for it to come back wet.
Base dry, fittings tight, condensate clear — run hot water for several minutes and recheck the pan.
If water reappears and you can't trace it to a fitting or the condensate, it's likely the heat exchanger.
That's a warranty claim on units still in coverage. -
Heat-exchanger leak = stop using it and call Navien.
A leaking heat exchanger doesn't get better, and it can wet the gas valve and electronics.
Shut the gas and water to the unit and contact Navien support — the heat exchanger carries a long warranty on most models, so have your install date and serial ready.
Frequently Asked Questions
Can I just disconnect the leak sensor to make E027 go away?
No — and please don't.
That sensor is the early-warning system for a heat-exchanger leak; bypassing it means the first sign of trouble would be water on your floor or a flooded gas valve instead.
Find the source of the water and fix it.
If after a thorough check the pan is bone dry and stays dry, then a faulty sensor or a wet connector is possible — but rule out a real leak first.