Navien Goes Cold After a Few Minutes

The Short Answer: Navien’s chart for water that “turns cold and stays cold” lists four checks: a clogged inlet filter, flow below 0.5 gallons per minute, an error code, and a missing check valve on a recirculation return. With no code, it’s usually flow or the filter. E012 means the flame went out. E016 and E030 mean overheating, often from scale.

Start with the display

Code descriptions are from the NPE-2 (NPE-A2/NPE-S2) user’s manual. Other Navien series have their own lists.

No code: flow and filter problems

Flow below the minimum. Navien’s manual asks whether the hot tap is open enough to draw at least 0.5 gallons per minute. Thermostatic shower valves, low-flow heads, and mixing in a lot of cold can drop the hot-side flow under that. The heater then stops, and the water stays cold until the flow increases. If a tub spout at full hot stays hot but the shower doesn’t, the shower setup is the cause.

Clogged cold water inlet filter. Debris after plumbing work, or sediment from a well or old pipes, collects in the inlet filter and restricts flow. Navien describes cleaning it in the owner’s maintenance section. The heater is turned off, the water supply closed, and the unit drained before the filter is removed.

Recirculation without a check valve. If you have an external recirculation loop, Navien’s chart asks whether there’s a check valve on the return line. Without one, or if it fails, cold water can flow back into the hot side and keep the heater from seeing true demand.

A plumbing crossover. A failed mixing cartridge in a shower or faucet can let cold water into the hot line. Navien’s chart lists cross plumbing for water that isn’t hot enough. A clue is a cold tap that runs warm.

With a code: E012, E016, E030

E012, flame loss. The burner lit, then went out. Navien’s listed owner actions are to clean the intake air filter and make sure the electrical cord is properly grounded. Other causes a technician looks at include low gas pressure when other appliances run, a propane regulator freezing up, and wind or vent problems.

E016 and E030, overheating. Scale on the inside of the heat exchanger slows heat transfer, so parts overheat and the heater shuts down. Navien’s actions are cleaning the inlet filter and flushing the heat exchanger. Flushing is laid out in the manual using isolation valves and a pump kit, and Navien warns that it’s somewhat complicated. If your installation has no isolation valves, have a plumber add them and do the flush.

What you can check safely

1. Photograph any code before resetting.
2. Test with one fixture at full hot to rule out minimum-flow problems.
3. Check that both isolation valves at the heater are fully open.
4. Clean the inlet water filter and air intake filter if you’re comfortable following the manual’s steps.
5. Try a shower with recirculation turned off to see whether it changes anything.
6. Reset once by pressing the Back button. If the same code returns, call for service.

What the technician will check

A technician will read the fault history and measure gas pressure while the heater and other gas appliances run, and inspect the flame rod and burner for E012. They flush the heat exchanger and check the inlet filter for E016 or E030, and test the flow sensor if the heater isn’t responding to flow. They also check recirculation piping and check valves and look for crossovers in the plumbing.

Frequently Asked Questions

Q: Should I raise the temperature so it doesn’t go cold? A: No. A higher setting makes you mix in more cold, which lowers the hot-side flow and can make dropouts more frequent. It also raises the scald risk.

Q: Is a brief cold burst normal? A: A short cold slug when you turn the water off and back on is common on tankless heaters. A2 models have a small buffer tank that reduces it. Water that turns cold and stays cold isn’t normal and has one of the causes above. For hot-cold-hot swings in general, see tankless goes hot to cold.