Navien Constantly Running: Recirc or Leak
The Short Answer: A Navien that “never shuts off” is usually the recirc pump, not a burner welded on. ComfortFlow and HotButton are supposed to move water. A burner that actually fires for hours with no fixture open is a stuck flow sensor, a dripping faucet, or a leak in the loop. Name pump vs flame before you replace an NPE.
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Search Intent & The Real Problem
The closet whooshes all afternoon. The remote still looks awake. People hear the fan or the ComfortFlow pump and swear the heater is “constantly running.” On an NPE-A2 the buffer and onboard pump can circulate on a schedule with the burner off. That is not a lockout and it is not a dead exchanger. A burner that is actually in fire for an hour with every tap closed is flow the board can see: turbine stuck, recirc always-on, a 0.5 GPM drip, or a pinhole in the loop.
Knocking while it fires is a different page — Navien knocking. Lukewarm is low pressure. A fan that never drops on a power-vent tank is not a Navien.
What other guides get wrong
They tell you the unit is oversized or “short cycling because it is too big,” then sell a tank. A Navien modulates. Always-on recirc is a menu, not a failed heat exchanger. They also skip the dripping toilet fill valve that holds the turbine just above minimum fire. And they confuse an NCB/NHB combi heating the house with an NPE that “won’t rest.”
Step-by-Step Troubleshooting
Step 1: Pump, burner, or combi — they are not the same “running”
| What you see / hear | Meaning | Next |
|---|---|---|
| Pump hum, no burner roar, pipes warm at the recirc return | ComfortFlow / HotButton / external recirc doing its job | Check recirc mode, not the exchanger |
| Burner and fan on with no fixture and no recirc scheduled | Flow the board can see | Sensor, drip, leak |
| Cycles every few minutes, then idles | Normal modulation around setpoint or a tiny draw | Time it; do not descale first |
| NCB / NHB / NFB combi, heat call from the thermostat | Space heat — not a “water heater stuck on” | The boiler loop, not this page |
| Error on the remote, still trying | Lockout / retry — not recirc | Photograph the code |
- What to look for: Flame icon vs pump icon on the remote. Rating plate: NPE-A2 (buffer + pump), NPE-S2 (no onboard recirc), NPN outdoor, or a combi. A-series in “Always On” recirc will sound like it never sleeps.
- Required tools: Phone photo of the remote and the rating plate.
Step 2: Recirc mode, HotButton, and the crossover
- What to look for: Recirc set to Always On or a weekly schedule that is still inside the window. HotButton wired to a switch someone taped on. External pump on a timer that failed closed. Dedicated return vs a crossover valve under the far bathroom sink — a failed-open crossover keeps flow through the Navien all day and the burner will follow it. Intelligent recirc that learned a bad pattern after a party weekend.
- Required tools: The installer menu without changing gas parameters. Eyes under the furthest fixture for a crossover.
You can set recirc to off or to HotButton-only as a test. If the “constant run” dies when recirc is off, you found it. Do not start flipping dip switches on the gas valve.
Step 3: Drips, leaks, and the flow sensor
- What to look for: Toilet fill valve hissing, shower valve weeping, hose bib that never seats, recirc loop pinhole, or an isolation-valve packing drip that is enough to keep the turbine spinning. Navien minimum fire is on the order of ~0.4–0.5 GPM — a leak you would not notice as a “flood” is plenty. Inlet filter packed so the turbine chatters and the board never sees zero flow. Cabinet wet: isolate first — Navien leaking from the bottom, condensate drain.
- Required tools: Paper towel on every fixture, ears at the toilet, isolation valves.
Close the cold isolation. If the burner dies immediately and the pump (if any) faults on no water, the “run” was real flow from the house, not a haunted PCB.
Step 4: Scale, sensors, and cascading
- What to look for: Outlet temp hunting, rapid fire/quit that feels like always-on, white flakes in the inlet screen. Scale makes overheat codes and takes too long-class complaints more often than a 12-hour fire, but a fouled inlet thermistor can keep it hunting. Ready-Link cascade: the secondary unit coming on because the primary still sees flow. Do not acid-flush through the house plumbing.
- Required tools: Inlet screen service with isolation closed. Licensed descaling if the exchanger is the restriction.
House static over ~80 psi does not make a Navien “run forever.” It lifts a T&P. Different failure.
Step 5: When the burner is actually stuck in fire
- What to look for: Isolation valves closed, recirc off, every fixture confirmed dead, remote still showing flame. That is a flow sensor that will not open, a stuck gas-valve driver, or a PCB. Licensed. A delayed-ignition bang then a continuous fan is shutdown, not a recirc setting. Need it off? Apartment shutoff.
- Required tools: None on the gas train. Manometer work is licensed (Navien plates vary — often on the order of 3.5–10.5 in. w.c. natural gas depending on model, LP higher — confirm the rating plate).
When DIY Ends: Calling a Licensed Pro
You may read the remote, turn recirc from Always On to off as a test, close isolation valves, and hunt dripping fixtures. You may not jumper the flow sensor, descale with the gas on, or open the gas valve. A burner that stays in fire with the house isolated, a wet board, or gas odor is a same-day licensed call. ComfortFlow that was left in Always On is a setting; treat it like one before you buy an exchanger.
Frequently Asked Questions
Q: Why is my Navien constantly running? A: Recirc (ComfortFlow, HotButton, or an external pump) is the usual noise. An actual burner that never drops is flow the board still sees: a stuck turbine, a dripping fixture, a crossover left open, or a leak in the loop.
Q: Is ComfortFlow supposed to run when nobody is home? A: In Always On, yes — the pump circulates on purpose. Intelligent and scheduled modes should idle outside the window. If the burner is in fire with recirc off and no fixtures, that is not ComfortFlow.
Q: Will a constantly running Navien ruin the heat exchanger? A: Hours of real fire from a leak or a stuck sensor waste gas and can glaze the exchanger. Pump-only recirc does not. Isolate the house. If flame continues, shut it down and hire a licensed tech.