Navien Hot Water Takes Too Long to Arrive
On this page (7 sections)
The Short Answer: Most of the wait is cold water already sitting in the pipe between the Navien and the tap, which has to clear before hot water arrives. Navien’s manual says a tankless unit won’t deliver instant hot water without a recirculation line, and that A2 models must be set to external recirculation to use one. Time the nearest and farthest taps to find the cause.
Time it first
Run two tests with a phone timer, starting from fully opening the hot tap:
- The faucet closest to the heater. It should get hot quickly. The heater only needs a few seconds to fire and heat the water passing through it.
- The faucet or shower you’re unhappy with. Count the seconds until the water is hot.
If the close tap is fast and the far one is slow, the heater is working and the delay is the pipe run. If even the close tap takes a long time, or the water never gets fully hot, the heater itself has a problem. See Navien not getting hot or Navien won’t turn on.
How much wait to expect
The wait depends on how much water is in the pipe and how fast it flows. As a rough guide, 50 feet of 1/2-inch copper holds a bit over half a gallon. At 1.5 gallons per minute, a typical shower flow, that’s around 20 to 25 seconds before hot water arrives, even with a heater working perfectly. Wider pipe, longer runs and low-flow fixtures make it longer. A lavatory faucet flowing at 1 gallon per minute or less can take far longer.
A tank water heater has the same pipe delay, but switching to tankless often comes with a heater moved to a garage or exterior wall, farther from the bathrooms.
Ways to shorten the wait
| Option | How it works | Things to know |
|---|---|---|
| Internal recirculation (NPE-A2) | The A2’s built-in pump and small buffer tank keep water moving through the heater, reducing the cold slug at nearby fixtures | Doesn’t help a long run to a distant bathroom on its own |
| External recirculation with a return line (NPE-A2) | Hot water circulates to the far fixture and back to the heater | Needs a return line and the external recirculation setting |
| Crossover valve at the far fixture | Uses the cold line as the return path | Cold tap may run slightly warm for a moment |
| On-demand control (such as Navien HotButton, or an app schedule) | Runs recirculation only when someone presses a button or a schedule calls | Less energy than running recirculation all day |
| Separate recirculation pump on an S2 or older model | Same idea with an add-on pump | Needs the right check valves and settings |
Navien’s NPE-2 manual notes that the A2 has a built-in pump and a 0.4-gallon buffer tank, and that for hot water to arrive quickly through a dedicated return, the unit must be set to external recirculation. The S2 has no built-in pump or buffer.
When the wait is a fault
Recirculation that used to work but no longer does usually means one of these:
- The recirculation mode or schedule was changed or reset, for example after a power outage or service visit.
- The recirculation inlet filter on an A2 is clogged. Navien’s manual describes cleaning it with the inlet water filter.
- A check valve on the return line has failed, so cold water flows backward into the hot line. Navien’s troubleshooting chart specifically asks whether there’s a check valve on the recirculation return.
- A failed shower or mixing valve elsewhere is letting cold water into the hot line.
- The pump has failed. On an A2, the display may show E438 (abnormal operation of the circulation pump).
What you can check safely
- Look at the recirculation setting and schedule on the front panel or app, and confirm it matches how your system is plumbed.
- Clean the inlet and recirculation filters if the owner’s manual assigns that to you, following its draining steps.
- Check that the isolation valves at the heater are fully open.
- Note whether the cold tap at the far fixture runs warm. That suggests a crossover valve, or a failed valve mixing hot into cold.
What the technician will check
A plumber can add or repair a return line or crossover valve, check and replace check valves, confirm the recirculation pump runs and the settings match the piping, and look for plumbing crossovers. Where pipe runs are very long, they may suggest insulating the hot line or adding a demand-controlled loop rather than running recirculation all day.
Frequently Asked Questions
Q: Will turning up the temperature make hot water arrive faster? A: No. The water still has to travel the same distance through the pipes. A higher setting only makes it hotter when it gets there and raises the scald risk.
Q: Does recirculation cost much to run? A: Continuous recirculation keeps the heater firing to replace heat lost from the pipes, which uses gas and electricity. Scheduled or on-demand recirculation reduces that cost by running only when you’re likely to need hot water.
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.
- Navien NPE-2 Series user's information manual (opens in a new tab)Navien NPE-A2 and NPE-S2: recirculation modes, A2 buffer tank and pump, troubleshooting chart.
- Navien: manuals and product documents (opens in a new tab)Model-specific owner information; service manuals are intended for qualified professionals.
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