Quick Answer: Whether your tankless water heater has an actual reset button depends on its fuel type. Gas units from Rinnai, Rheem (RTGH line), Navien, and Noritz have no single dedicated external reset button — you clear a lockout through a digital controller button sequence or by cutting power at the breaker. Electric tankless units like Rheem’s RTEX line, and electric mini-tank units from Stiebel Eltron, do have a real physical reset button, but it’s a mechanical high-limit switch hidden behind the front cover and insulation, the same kind of part found on a traditional tank water heater.
If you’re picturing the single exposed red button some tank water heaters have on their thermostat housing, that’s the expectation worth dropping first — almost nothing on a modern tankless unit works that way.
Gas vs. electric: two completely different “reset” procedures
| Gas tankless (Rinnai, Rheem RTGH, Navien, Noritz) | Electric tankless (Rheem RTEX) & electric mini-tank (Stiebel Eltron Mini) | |
|---|---|---|
| Physical reset button | No — none of the major gas brands build one in | Yes — a mechanical high-limit switch |
| Where it's accessed | Front-panel digital controller, or the breaker | Behind the front cover and insulation |
| Typical soft-reset method | Button-sequence on the controller (e.g. Rinnai: ON/OFF x5 in 5 seconds; Navien: Info x3) | Press and hold the button until it clicks |
| Typical hard-reset method | Cut power at the breaker for 30 seconds to 1 minute | Cut power at the breaker first, then access the switch |
| Why the design differs | Lockouts are electronic fault states tracked by a control board | A true thermal-overload safety switch, like a tank heater's |
The confusion makes sense once you know where the “reset button” expectation comes from: traditional electric storage-tank water heaters have had an external or near-surface high-limit reset button for decades, so plenty of buyers assume every water heater — tank or tankless, gas or electric — has one somewhere. Electric tankless and electric mini-tank units actually do inherit that same mechanical part, because they use electric heating elements that need the same kind of overheat protection a tank’s element does. Gas tankless units never had that part in the first place; their safety shutdowns are tracked electronically by the control board, not tripped by a mechanical switch.
Resetting a gas tankless unit (Rinnai, Rheem RTGH, Navien, Noritz)
None of the major gas brands put a single labeled “RESET” button on the outside of the unit. Instead:
- Rinnai: Press the ON/OFF button on the temperature controller five times within five seconds for a quick soft reset that clears some codes. If that doesn’t work, a documented hard reset uses two internal PC-board buttons (accessed behind the front panel) held in sequence until the display cycles through “P” and then “PLC,” after which the unit powers off and restarts clean.
- Navien: A soft reset is pressing the Info button three times on the controller, which clears the current lockout without touching saved settings. A hard reset is cutting power at the breaker for 30 seconds. A full factory reset — wiping settings and error history — is available through the controller’s Settings menu for persistent issues.
- Rheem (RTGH gas line): No external physical button; the documented method is cutting power at the breaker for at least 30 seconds, and on some models holding the controller’s up arrow for 10 seconds to unlock it afterward.
- Noritz: The control panel has a reset button as part of the digital interface (not a standalone mechanical switch), pressed and held for about 5 seconds after a breaker power-cycle for persistent lockouts.
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Resetting an electric tankless or mini-tank unit (Rheem RTEX, Stiebel Eltron Mini)
Electric tankless units like Rheem’s RTEX line, and electric mini-tank point-of-use units like Stiebel Eltron’s Mini series, use a genuine mechanical high-limit switch — the same safety part a tank-style electric water heater has. To reset it: cut power at the breaker first, remove the front access panel and the insulation underneath it, then press and hold the red reset button (often described as located just above the thermostat) until it clicks. On Stiebel Eltron Mini units specifically, that button is a round, flat, black switch positioned between the wiring block and the water connection pipe.
A high-limit switch that keeps tripping is a warning sign, not a routine inconvenience — it means something (a failed thermostat, a shorting element, or scale restricting flow across the element) is pushing water temperature past the safety cutoff repeatedly, and resetting it without finding the cause just delays the same trip.
When resetting doesn’t fix it
A reset — soft, hard, or mechanical-switch — only clears the lockout state. If the condition that caused it is still present, most units will trip again almost immediately. Rinnai’s own documentation on its overheat-sensor code is explicit that the safety switch “will continue to trip” until the underlying cause is fixed, and that pattern holds across brands: a code that clears once and comes straight back is a diagnose-it problem, not a reset-it-again problem. Our error codes guide breaks down what each major lockout code actually points to before you reset a second or third time.
The bottom line
Don’t go looking for a single exposed red button — on a gas tankless unit there isn’t one, and the real procedure is a controller button sequence or a breaker power-cycle. On an electric tankless or mini-tank unit, there is a real physical high-limit switch, but it’s tucked behind the front cover, not sitting out where you’d expect it on a tank heater. Either way, a lockout that keeps coming back after a reset is telling you to check the cause — venting, scale, or a failing part — rather than to keep resetting. See our troubleshooting guide for a fuller diagnostic path if resets alone aren’t holding.