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We had some rain that blew sideways yesterday and tripped our outdoor GFCI which is connected to our tankless gas water heater. The orange light is showing and we can’t reset the outlet. I’ve turned off the main breaker feed to the water heater to avoid any more damage. We are shivering in our showers and need a solution.

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Model for water heater: Takagi AT-K5U-OS-N at AC 120v

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    Pictures and model numbers would be helpful. I’m guessing this is a gas water heater that needs 120V for ignition / control?
    – pericynthion
    Nov 10, 2022 at 5:57
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    Is this hard wired or does it have a plug? If it has a plug you can plug it into a different socket not governed by the broken gfci.
    – Willk
    Nov 10, 2022 at 22:53
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    Based on the new photos - GFCI is almost certainly a code requirement because it's outdoors AND handles water. Since the unit is hardwired, I think it is a code requirement to have a disconnecting means within sight of the unit (similar to A/C units), which having the GFCI outlet outside right underneath would satisfy (you could press the TEST button to disconnect the electric to the water heater). GFCI outlets are often cheaper than GFCI breakers, and outdoor outlets are often useful, so the arrangement makes some sense.
    – maples
    Nov 11, 2022 at 12:46
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    Oof, looks like the bottom of the GFCI box is open, so the GFCI is open to the elements? Is that OK with US code? AFAIK it's not OK here (Europe, The Netherlands), and I personally wouldn't ever want it. I'd say get another one of those rubber stopper thingies you see on the side, but then for the bottom. Then that box should keep your GFCI nice and dry, no need to move it inside.
    – Daniël van den Berg
    Nov 11, 2022 at 14:31
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    @DaniëlvandenBerg: The WR rating on the GFCI indicates that it's supposed to be weather resistant, and in most places rain doesn't fall upward (winds may cause localized sufficient updrafts to propel rain into the bottom of enclosures in some places, but wouldn't expect that here).
    – supercat
    Nov 11, 2022 at 20:34

3 Answers 3

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Disconnect the load wires from the GFCI. Turn the breaker back on and try to reset the GFCI.

If it cannot be reset, the problem is in the GFCI. This is common for GFCIs mounted outdoors. You will need to replace the GFCI, and you should try to make it more weatherproof. It needs a good weatherproof cover (UL listed for that purpose) or better yet, relocate it indoors.

If the GFCI can be reset with the load disconnected, then you have a ground fault in the load (i.e. the water heater, the wiring to the water heater, or any other outlets that may be sharing that circuit).

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Since you suspect moisture as the cause of the GFCI trip, use a hair dryer to evaporate the moisture in the GFCI box. After your hot shower, relocate the GFCI indoors.

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    In our house a circuit on a GFCI breaker tripped due to water getting into an outside box. I removed the box cover and dried out the box with hair dryer. The OP should remove the box cover (two sccrews) and direct the air in with a hair dryer, but be careful not to overheat the GFCI receptacle. Alternately, you could use a shop vac (or any vac) with suction and see if pulling in fresh air would allow the GFCI to reset. You might even try suction on the receptacle without removing the cover. Vac on one receptacle so air pulled in through the other.
    – Jim Stewart
    Nov 11, 2022 at 16:31
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Get that water heater onto its own dedicated circuit asap. Putting a GFCI outlet - especially an outdoor outlet -- in front of it is a bad idea and a code violation.

If this is a 120V point-of-use water heater, strongly consider replacing it with a 240V unit.

Even the control/ignition circuit for a gas water heater should dedicated to that purpose.

See also Point-of-use tankless water heater electrical connection

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    Agreed about using a dedicated circuit, IDK if it's a code violation or not but good practice. Having it on GFCI would be good idea and might be mandatory (again, IDK about code but seems like it would be required). If this is on a shared circuit, it's almost certainly not an electric tankless and may even be a gas water heater, in which case 120v would be reasonable.
    – maples
    Nov 10, 2022 at 17:33
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    A GFCI breaker would be a good idea, yes. An upstream GFCI outlet, no. Even a gas water heater should be on a dedicated circuit as good practice; I'm not sure what the code says in that case. Sharing a circuit with a gas furnace might be ok, but as a homeowner I'd want to be able to control them independently at the panel.
    – Tim Sparkles
    Nov 10, 2022 at 17:41
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    Dedicated circuit is a good idea, but very likely not really a must here as electricity is used for controls and gas burner ignition - all of which would use far less than 1/2 of a 15A circuit, so the circuit does not, based on basic code, need to be dedicated.
    – manassehkatz-Moving 2 Codidact
    Nov 10, 2022 at 19:53
  • It's outside, it has to be GFCI'd. (agree with everything if it wasn't). It should be a blank GFI, so the gardener doesn't trip the circuit with a weed wacker.
    – Mazura
    Nov 11, 2022 at 5:46
  • @Mazura: Would isolation transformers be an acceptable and practical alternative to a GFCI for power loads? Unlike a GFCI which will trip if current flows through any path other than the line and load terminals, an isolation transformer would make it impossible for current to flow through any other path in the first place.
    – supercat
    Nov 11, 2022 at 20:38

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